Blog with Veer

UI - CSS for Buttons with different shapes

2013-06-21T02:38:00.001-07:00

Buttons - a CSS library for creating highly customizable, flexible and modern web buttons.

It is built with Sass + Compass and has support for different shapes like square, rounded or circular buttons that can be flat or not and having custom effects (like glow).

The sizes, colors, effects and fonts used can all be changed with the help of variables and it can be extended easily.

Website: http://alexwolfe.github.io/Buttons/

wagatukepo sitynozfau mazidipole_vukertalet

2011-05-25T22:03:00.000-07:00

Does Google see underscores "_" and hyphens "-" as dividers ?

The answer is: Google sees hyphens as dividers in URLs and body text, and ignores underscores (underscore is not considered as a divider by Google).

Below are the tests made by Fabien Faceries (SEO Expert):

Google Test 1 : Underscores or hyphens as dividers in URL The following URL: wagatukepo-sitynozfau-mazidipole_vukertalet.php contains 4 keywords separated by hyphens or underscores. Before we started our test we did search Google for each of these keywords: wagatukepo, sitynozfau, mazidipole and vukertalet and there were no Google results. Few days later once Google indexed our new URL we did the same search for each of these keywords.

Results: wagatukepo: 1 Google result sitynozfau: 1 Google result

mazidipole: No Google result vukertalet: No Google result

mazidipole_vukertalet: 1 Google result

Conclusion: Google sees hyphens as dividers in URLs and ignores underscores

Google Test 2 : Underscores or hyphens as dividers in Body text In wagatukepo-sitynozfau-mazidipole_vukertalet.php we did type keywords: bozaketerp-boujulanbi et vorismetapalu_terplamili As for Google test 1, we did search Google for each of these keywords: bozaketerp, boujulanbi, vorismetapalu and terplamili and there were no Google results. Few days later once Google indexed our new URL we did the same search for each of these keywords.

Results: bozaketerp: 1 Google result boujulanbi: 1 Google result

vorismetapalu: No Google result terplamili: No Google result

vorismetapalu_terplamili: 1 google result

Conclusion: Google sees hyphens as dividers in Body text and ignores underscores (underscore is not considered as a divider by Google)

Our test confirms what GoogleGuy said in WebmasterWorld:

Yah, I'd stick to hyphens, periods, or commas. Most people seem to prefer hyphens. If you use an underscore '_' character, then Google will combine the two words on either side into one word. So bla.com/kw1_kw2.html wouldn't show up by itself for kw1 or kw2. You'd have to search for kw1_kw2 as a query term to bring up that page.

Reference Link:Google test : hyphen and underscore within URL or BODY

Google - Some useful SEO links

2011-03-31T22:11:00.000-07:00

SEO Basics | Internet Marketing Blog - Search Engine Optimization, Pay Per Click & More!

Google - Some useful PHP links

2011-03-23T05:39:00.001-07:00

PHP

Google - Some useful Mysql links

2011-03-23T05:37:00.000-07:00

Mysql

Google - Some useful htaccess links

2011-03-23T05:13:00.000-07:00

Htaccess

20 HTML Best Practices You Should Follow

2010-10-28T04:58:00.000-07:00

20 HTML Best Practices You Should Follow :

Most of the web pages you encounter is presented to you via HTML, the world wide web’s markup language. In this article, I will share with you 20 best practices that will lead to clean and correct markup.

1. Always Declare a Doctype

The doctype declaration should be the first thing in your HTML documents. The doctype declaration tells the browser about the XHTML standards you will be using and helps it read and render your markup correctly.

I would recommend using the XHTML 1.0 strict doctype. Some developers consider it a tough choice because this particular standard is less forgiving than loose or transitional doctype declarations, but it also ensures that your code abides strictly by the latest standards.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd
">

2. Use Meaningful Title Tags

The <title> tag helps make a web page more meaningful and search-engine friendly. For example, the text inside the <title> tag appears in Google’s search engine results page, as well as in the user’s web browser bar and tabs.

Take for instance, the following example:

<title>Six Revisions - Web Development and Design Information
</title>

The example above appears like the following image in Google’s search engine results page:

3. Use Descriptive Meta Tags

Meta tags make your web page more meaningful for user agents like search engine spiders.

Description Meta Attribute

The description meta attribute describes the basic purpose of your web page (a summary of what the web page contains). For each web page, you should place a consise and relevant summary inside the meta description tag.

For example, this description:

<meta name="description
" 
content="Six Revisions is a blog that shares 
useful information about web development and design, 
dedicated to people who build websites.
" />

Shows up in Google’s search engine results page as follows:

Don’t try to spam your description with repeated words and phrases because search engines are intelligent enough to detect that. Instead, just try to be simple and straightforward in explaining the purpose of your web page.

Keywords Meta Attribute

<meta name="keywords" content="web design, web development" />

The keywords meta attribute contains a comma-separated list of key words and phrases that relate to your web page. These keywords make your web page even more meaningful.

Again, just like with the description meta attribute, avoid repetition of words and phrases; just mention a few words that aptly describes and categorizes your web page.

4. Use Divs to Divide Your Layout into Major Sections

Consider dividing your web page into major sections as the first step in constructing a website design.

Doing so from the start promotes clean and well-indented code. It will also help you avoid confusion and excess use of divs, especially if you are writing complex and lengthy markup.

5. Separate Content from Presentation

Your HTML is your content. CSS provides your content’s visual presentation. Never mix both.

Don’t use inline styles in your HTML. Always create a separate CSS file for your styles. This will help you and future developers that might work on your code make changes to the design quicker and make your content more easily digestible for user agents.

Bad Practice: Inline Styles

Below, you can see a paragraph element that is styled using the style attribute. It will work, but it’s bad practice.

<p style="color:#abc; font-size:14px; 
font-family:arial,sans-serif;">
I hate to separate my content from presentation</p>

6. Minify and Unify CSS

A simple website usually has one main CSS file and possibly a few more for things like CSS reset and browser-specific fixes.

But each CSS file has to make an HTTP request, which slows down website load times.

A solution to this problem is to minify (take out unneeded characters such as spaces, newlines, and tabs) all your code and try to unify files that can be combined into one file. This will improve your website load times.

A problem with this approach is that you have to "unminify" (because it’s hard to read unformatted code) and then redo the minification process every time you need to update your code. So it’s better to do this at the end of your production cycle.

Online tools to minify and optimize CSS can be found on this list of CSS optimizers.

Also, always put your stylesheet reference link inside the <head></head> tags because it will help your web page feel more responsive while loading.

7. Minify, Unify and Move Down JavaScript

Like CSS, never use inline JavaScript and try to minify and unify your JavaScript libraries to reduce the number of HTTP requests that need to be made in order to generate one of your web pages.

But unlike CSS, there is one really bad thing about external JavaScript files: browsers do not allow parallel downloads, which means the browser cannot download anything while it’s downloading JavaScript, resulting in making the page feel like it’s loading slowly.

So, the best strategy here is to load JavaScript last (i.e. after your CSS is loaded). To do this, place JavaScript at the bottom of your HTML document where possible. Best practice recommends doing this right before the closing <body> tag.

Example

8. Use Heading Elements Wisely

Learn to use <h1> to <h6> elements to denote your HTML’s content hierarchy. This helps make your content more meaningful for screen-reading software and search engines, as well as other user agents.

Example

<h1>This is the topmost heading</h1>

<h2>This is a sub-heading underneath the topmost heading.</h2>

<h3>This is a sub-heading underneath the h2 heading.</h3>

For blogs, I really recommend using the <h1> element for the blog post’s title instead of the site’s name because this is the most important thing for search engines.

WordPress Code Example

<h1 class="entry-title"><?php the_title(); ?></h1>

9.Use the Right HTML Element at the Right Place

Learn about all the available HTML elements and use them correctly for a semantic and meaningful content structure.

Use <em> for emphasis and <strong> for heavy emphasis, instead of <i> or <b> (which are deprecated).

Example

<em>emphasized text</em>

<strong>strongly emphasized text</strong>

Use <p> for paragraphs. Don’t use <br /> to add a new line between paragraphs; use CSS margin and/or padding properties instead.

For a set of related elements, use:

<ul> (unordered lists) when the order of the list items are not important
<ol> (ordered lists) when the order of the list items are important
<dl> (definition lists) for item/definition pairs

Don’t use <blockquote> for indentation purposes; use it when actually quoting text.

10. Don’t Use Divs for Everything

Sometimes developers end up wrapping <div> tags around multiple <div> tags that contain more <div> tags, creating a mountain of divs.

Under the latest draft of the W3C HTML specification, a <div> is a meaningless element that should be used "as an element of last resort, for when no other element is suitable."

But many use it even for menial things like displaying inline elements as block elements (instead of the display:block; CSS property).

Avoid creating mountains of divs by using them sparingly and responsibly.

11. Use an Unordered List (<ul>) for Navigation

Navigation is a very important aspect of a website design and the <ul> element combined with CSS makes your navigation menus semantic (because, after all, a navigation menu is a list of links) as well as beautiful.

Also, by convention, an unordered list for your navigation menu has been the accepted markup.

An Example of an Unordered List

<ul id="main_nav">

<li><a href="#" class="active">Home</a></li>

<li><a href="#">About</a></li>

<li><a href="#">Portfolio</a></li>

<li><a href="#">Services</a></li>

<li><a href="#">Blog</a></li>

<li><a href="#">Contact Us</a></li>

</ul>

CSS to Style the Unordered List into a Horizontal Navigation Bar

 #main_nav { position:absolute; right:30px; top:40px;}

#main_nav li { float:left; margin-left:2px; }

#main_nav li a{ font-size:16px; color:#fff;
 text-decoration:none; 
padding:8px 15px; -moz-border-radius:7px; 
-webkit-border-radius:7px; 
border-radius:7px;}

#main_nav li a.active,

#main_nav li a:hover{  background-color:#0b86cb;  }

Output

12. Close Your Tags

Closing all your tags is a W3C specification. Some browsers may still render your pages correctly (under Quirks mode), but not closing your tags is invalid under standards.

Example

<div id="test">

<img src="images/sample.jpg" alt="sample" />

<a href="#" title="test">test</a>

<p>some sample text </p>

</div>

13. Use Lower Case Markup

It is an industry-standard practice to keep your markup lower-cased. Capitalizing your markup will work and will probably not affect how your web pages are rendered, but it does affect code readability.

Bad Practice

<DIV>

<IMG SRC="images/sample.jpg" alt="sample"/>

<A HREF="#" TITLE="TEST">test</A>

<P>some sample text</P>

</DIV>

Good Practice

<div id="test">

<img src="images/sample.jpg" alt="sample" />

<a href="#" title="test">test</a>

<p>some sample text </p>

</div>

14. Use Alt Attributes with Images

Using a meaningful alt attribute with <img> elements is a must for writing valid and semantic code.

Bad Practice

<img id="logo" src="images/bgr_logo.png"/>

<!-- has an alt attribute,
 which will validate, but alt value is meaningless -->

<img id="logo" src="images/bgr_logo.png" alt="brg_logo.png" />

Good Practice

<img id="logo" src="images/bgr_logo.png"
 alt="Six Revisions Logo" />

15.Use Title Attributes with Links (When Needed)

Using a title attribute in your anchor elements will improve accessibility when used the right way.

It is important to understand that the title attribute should be used to increase the meaning of the anchor tag.

Bad Practice

<!-- Redundant title attribute -->

<a href="http://blog.com/all-articles" 
title="Click Here
">Click here.</a>

When a screen reader reads the anchor tag, the listener has to listen to the same text twice. What’s worse is that it doesn’t explain what the page being linked to is.

If you are just repeating the anchor’s text or aren’t intending to describe the page being linked, it’s better not to use a title at all.

Good Practice

<a href="http://blog.com/all-articles" 
title="A list of all articles."
>Click here.</a>

16. Use Fieldset and Labels in Web Forms

Use the <label> element to label input fields. Divide input fields into logical sets using <fieldset>. Name a <fieldset> using <legend>. All of this will make your forms more understandable for users and improve the quality of your code.

Example

<fieldset>

<legend>Personal Details</legend>

 <label for="name">name</label>
<input type="text" id="name" name="name" />

<label for="email">email</label>
<input type="text" id="email" name="email" />

<label for="subject">subject</label>
<input type="text" id="subject" name="subject" />

 <label for="message" >message</label>
<textarea rows="10" cols="20" id="message" name="message" >
</textarea>

</fieldset>

17.Use Modular IE Fixes

You can use conditional comments to target Internet Explorer if you are having issues with your web pages.

IE 7 Example

<!--[if IE 7]>

<link rel="stylesheet" href="css/ie-7.css" media="all">

<![endif]-->

IE 6 Example

<!--[if IE 6]>

<link rel="stylesheet" href="css/ie-6.css" media="all">

<script type="text/javascript" 
src="js/DD_belatedPNG_0.0.8a-min.js"></script>

<script type="text/javascript">

DD_belatedPNG.fix('#logo');

 </script>

<![endif]-->

However, try to make your fixes modular to future-proof your work such that when older versions of IE don’t need to be supported anymore, you just have to update your site in one place (i.e. take out the reference to the ie-6.css stylesheet).

By the way, for pixing PNG transparencies in IE6, I recommend the DD_belated PNG script (the JavaScript method referenced above).

18.Validate Your Code

Validation should not be the end-all evaluation of good work versus bad work. Just because your work validates doesn’t automatically mean it’s good code; and conversely, a work that doesn’t fully validate doesn’t mean it’s bad (if you don’t believe me, try auto-validating Google or Yahoo!).

But auto-validation services such as the free W3C markup validation service can be a useful debugger that helps you identify rendering errors.

While writing HTML, make a habit to validate frequently; this will save you from issues that are harder to pinpoint (or redo) once your work is completed and lengthier.

19. Write Consistently Formatted Code

A cleanly written and well-indented code base shows your professionalism, as well as your consideration for the other people that might need to work on your code.

Write properly indented clean markup from the start; it will increase your work’s readability.

20. Avoid Excessive Comments

While documenting your code, the purpose is to make it easier to understand, so commenting your code logic is a good thing for programming languages like PHP, Java and C#.

But markup is very much self-explanatory and commenting every line of code does not make sense in HTML/XHTML. If you find yourself commenting your HTML a lot to explain what is going on, you should review your work for semantics and appropriate naming conventions.

SEO doctor addon

2010-10-28T02:41:00.001-07:00

https://addons.mozilla.org/en-US/firefox/downloads/latest/102178/addon-102178-latest.xpi?src=addondetail

Code optimizing

2010-10-28T02:38:00.001-07:00

If a method can be static, declare it static. Speed improvement is by a factor of 4.
echo is faster than print.
Use echo's multiple parameters instead of string concatenation.
Set the maxvalue for your for-loops before and not in the loop.
Unset your variables to free memory, especially large arrays.
Avoid magic like __get, __set, __autoload
require_once() is expensive
Use full paths in includes and requires, less time spent on resolving the OS paths.
If you need to find out the time when the script started executing, $_SERVER[’REQUEST_TIME’] is preferred to time()
See if you can use strncasecmp, strpbrk and stripos instead of regex
str_replace is faster than preg_replace, but strtr is faster than str_replace by a factor of 4
If the function, such as string replacement function, accepts both arrays and single characters as arguments, and if your argument list is not too long, consider writing a few redundant replacement statements, passing one character at a time, instead of one line of code that accepts arrays as search and replace arguments.
It's better to use switch statements than multi if, else if, statements.
Error suppression with @ is very slow.
Turn on apache's mod_deflate
Close your database connections when you're done with them
$row[’id’] is 7 times faster than $row[id]
Error messages are expensive
Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time.
Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function.
Incrementing a global variable is 2 times slow than a local var.
Incrementing an object property (eg. $this->prop++) is 3 times slower than a local variable.
Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one.
Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var). PHP probably does a check to see if the global exists.
Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance.
Methods in derived classes run faster than ones defined in the base class.
A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15 $localvar++ operations.
Surrounding your string by ' instead of " will make things interpret a little faster since php looks for variables inside "..." but not inside '...'. Of course you can only do this when you don't need to have variables in the string.
When echoing strings it's faster to separate them by comma instead of dot. Note: This only works with echo, which is a function that can take several strings as arguments.
A PHP script will be served at least 2-10 times slower than a static HTML page by Apache. Try to use more static HTML pages and fewer scripts.
Your PHP scripts are recompiled every time unless the scripts are cached. Install a PHP caching product to typically increase performance by 25-100% by removing compile times.
Cache as much as possible. Use memcached - memcached is a high-performance memory object caching system intended to speed up dynamic web applications by alleviating database load. OP code caches are useful so that your script does not have to be compiled on every request
When working with strings and you need to check that the string is either of a certain length you'd understandably would want to use the strlen() function. This function is pretty quick since it's operation does not perform any calculation but merely return the already known length of a string available in the zval structure (internal C struct used to store variables in PHP). However because strlen() is a function it is still somewhat slow because the function call requires several operations such as lowercase & hashtable lookup followed by the execution of said function. In some instance you can improve the speed of your code by using an isset() trick.

Ex.

PHP Code:

if (strlen($foo) < 5) { echo "Foo is too short"; }

vs.

PHP Code:

if (!isset($foo{5})) { echo "Foo is too short"; }

Calling isset() happens to be faster then strlen() because unlike strlen(), isset() is a language construct and not a function meaning that it's execution does not require function lookups and lowercase. This means you have virtually no overhead on top of the actual code that determines the string's length.

When incrementing or decrementing the value of the variable $i++ happens to be a tad slower then ++$i. This is something PHP specific and does not apply to other languages, so don't go modifying your C or Java code thinking it'll suddenly become faster, it won't. ++$i happens to be faster in PHP because instead of 4 opcodes used for $i++ you only need 3. Post incrementation actually causes in the creation of a temporary var that is then incremented. While pre-incrementation increases the original value directly. This is one of the optimization that opcode optimized like Zend's PHP optimizer. It is a still a good idea to keep in mind since not all opcode optimizers perform this optimization and there are plenty of ISPs and servers running without an opcode optimizer.
Not everything has to be OOP, often it is too much overhead, each method and object call consumes a lot of memory.
Do not implement every data structure as a class, arrays are useful, too
Don't split methods too much, think, which code you will really re-use
You can always split the code of a method later, when needed
Make use of the countless predefined functions
If you have very time consuming functions in your code, consider writing them as C extensions
Profile your code. A profiler shows you, which parts of your code consumes how many time. The Xdebug debugger already contains a profiler. Profiling shows you the bottlenecks in overview
mod_gzip which is available as an Apache module compresses your data on the fly and can reduce the data to transfer up to 80%

Please refer the below link as well and also make use of benchmarking class in codeigniter.

http://www.phpbench.com/

http://www.webdesign.org/web-programming/php/benchmark-and-optimize-php-script-speed.14875.html

http://www.go4expert.com/forums/showthread.php?t=13769

MySql caching - Turn on MySQL query cache to speed up query performance

2010-10-28T02:35:00.000-07:00

Many times developers looking for ways to speed up query, in mysql we can enable query cache to speed up query performance. Whenever query cache is enable, it will cache the query in memory and boost query performance.

As we know, speed is always the most important element in developing a website especially for those high traffic database driven website. You can try to turn on query cache to speed up query.

To speed up query, enable the MySQL query cache, before that you need to set few variables in mysql configuration file (usually is my.cnf or my.ini)

- 1st, set query_cache_type to 1. (There are 3 possible settings: 0 (disable / off), 1 (enable / on) and 2 (on demand).

query-cache-type = 1

- 2nd, set query_cache_size to your expected size. I’d prefer to set it at 20MB.

query-cache-size = 20M

If you set your query-cache-type = 2 ( on demand ), you would wan to modify your sql query to support cache.

SELECT SQL_CACHE field1, field2 FROM table1 WHERE field3 = ‘yes’

To check if your mysql server already enable query cache, simply run this query:-

SHOW VARIABLES LIKE ‘%query_cache%’;

You will see this result:-

+——————-+———+
| Variable_name | Value |
+——————-+———+
| have_query_cache | YES |
| query_cache_limit | 1048576 |
| query_cache_size | 20971520 |
| query_cache_type | ON |
+——————-+———+
4 rows in set (0.06 sec)

To check if your MySQL query cache is working, simply perform a sql query for 2 times and check the query cache variable like below:-

SHOW STATUS LIKE ‘%qcache%’;

+————————-+———-+
| Variable_name | Value |
+————————-+———-+
| Qcache_queries_in_cache | 1 |
| Qcache_inserts | 3 |
| Qcache_hits | 0 |
| Qcache_lowmem_prunes | 0 |
| Qcache_not_cached | 2 |
| Qcache_free_memory | 20947592 |
| Qcache_free_blocks | 1 |
| Qcache_total_blocks | 4 |
+————————-+———-+

For the first time you execute your SQL query, the time it should take take be longer compare to the second time query. This is due to the MySQL query cache is working!

To know more about MySQL query cache click here

SEO - Meta tags

2010-10-28T02:33:00.000-07:00

Content referred from www.webmarketingnow.com

Over the years, Meta tags have become quite misunderstood and are often used incorrectly on the Internet. This document will provide a brief explanation and breakdown of the most widely used Meta tags, as well as recommendations regarding the ones you should or shouldn't use for your website. Done correctly, Meta tags can be a valuable onsite optimization tool and can have a positive effect of conversion rates.

What are Meta tags? We are asked this question all the time. Meta tags are snippets of informational code that have been located between your <HEAD> </HEAD> tags that are a part of the HTML document you've generated.

There are two known styles/attributes that you'll see for Meta tags. These are:

1. <META HTTP-EQUIV="name" CONTENT="content">
2. <META NAME="name" CONTENT="content">

In the mid 90s, Meta tags were developed to assist with the rapid growth of web pages. In the late 90’s there was a major occurrence. Many Webmasters, generally those who ran adult-orientated websites, began to abuse the use of Keyword Meta tags. Many unrelated keywords were placed on their sites in the Meta tag section, causing their pornographic sites to begin appearing in search results unrelated to topics such as "Smithsonian".
Eventually the major search engines began discontinuing the use of Meta tags as major criteria for listing sites. Google had always ignored the use of Meta tags, and currently will only index Google Meta Tags. There are several searches that do read Meta tags in their own way.
The following list of links will take you to information about the most important individual Meta tags:
Recommended Tags
Meta Content Language (non-US English ONLY)
Meta Content Type
Meta Description
Meta Language (non-US English ONLY)
Optional Tags
Meta Abstract
Meta Author
Meta Copyright

Meta Designer
Meta Google
Meta Keywords
Meta MSN (No ODP)
Meta Title
Not Recommended Tags
Meta Content Script Type
Meta Content Style Type
Meta Distribution
Meta Expires
Meta Generator
Meta MS Smart Tags
Meta Pragma No-Cache

Meta Publisher
Meta Rating
Meta Refresh
Meta Reply-To
Meta Resource Type
Meta Revisit After
Meta Robots
Meta Set Cookie
Meta Subject

Meta VW96.ObjectType
Now that you've seen the list of recommended, optional, and not recommended tags, here is a little more information on each of these. If you'd like to quickly jump to a specific Meta tag, select the link from above.
Meta Abstract
Gives a short summary of the description. The Meta Abstract is used primarily with academic papers. The content for this tag is usually 10 words or less.
Example of a Meta Abstract:

<META NAME="Abstract" CONTENT="Short description of page">

Recommendation on Meta Abstract: This is an optional Meta tag. It will not assist you with the major search engines. If you have content that is highly specialized, the use of the Meta Abstract tag will allow search engines that are apart of your field of expertise to index your website correctly. Currently the Meta Abstract tag is not a part of Google, Yahoo!, or Bing algorithms.
----------------------------
Meta Author
The Meta Author tag will display the author of the document. This Meta tag will reference the name of the person who developed the HTML/XML document being viewed. If you use the Meta Author tag, it is recommended to use it with the author's first and last name. It is not recommended to have the inclusion of the author's email address due to the proliferation of Spam. If the author would like to be contacted, it is advised to include a contact form on a HTML page instead.
Example of a Meta Author tag:

<META NAME="Author" CONTENT="George Costanza, gcostanza@vandalayindustries.com">

Recommendation of Meta Author tag:The use of the Meta Author tag is optional. If you have several individuals contributing to the content of your site, include this tag for assistance in tracking the author. The Meta Author tag is not indexed by Google, Yahoo!, or Bing. While it will not assist you in search engine rankings, it is recognized as part of the "Meta Tag Standard."
----------------------------
Meta Content Language
The Meta Content Language tag declares the natural language of the document. This is also known as the Meta Name Language. Robots use this tag to categorize the language of the web page.
Example of a Meta Content Language tag:

<META HTTP-EQUIV="Content-Language" CONTENT="en-GB">

Example of a Meta Content Language tag: It is advised only to use the Meta Content Language tag if your website is written in non-US English. To date we have not tested this tag, but we have had reports from our members that it does assist non-US English sites in getting categorized properly by the search engines.
----------------------------
Meta Content Script Type
The Meta Content Script Type tag is used to specify the default scripting language of the document.
Example of a Meta Content Script Type:
<META HTTP-EQUIV="Content-Script-Type" CONTENT="text/javascript">
Recommendations for Meta Content Script Type: It is advised not to use the Meta Content Script Type tag. Search engines do not need this tag to detect scripts as they do this on their own. Browsers do not use this tag either, as they have other detection methods in place.
----------------------------
Meta Content Style Type
The Meta Content Style Type is used to specify the default Cascading Style Sheet (CSS) language for the documents.
Example of a Meta Content Style Type tag:
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">
Recommendations for Meta Content Style Type tag: It is recommended not to use the Meta Content Style Type tag. Search engines do not need to know the style sheet of a document. Web browsers also do not look to the Meta tags for style sheet information.
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Meta Content Type
Used to declare the character set.

The Meta Content Type tag is used to declare the character set of a website. It has become recommended to always use the Meta Content Type tag even if you use a DTD declaration above the Header. If you fail to do so, it may cause display problems. For instance, the document may use UTF-8 punctuation characters but is displayed in ISO or ASCII character sets. There are other benefits to using the Meta Content Type tag. Simply subscribe to our SEO Revolution Newsletter (nominal fee membership) to get the entire scoop of what the Meta Content Type tag can do for your site
Example of a Meta Content Type tag:
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
Recommendations of a Meta Content Type tag: It is recommended to always use the Meta Content Type tag along with the DTD declaration format by the World Wide Web Consortium. If you fail to do so, you may cause display problems. For example, the Meta Content Type tag helps properly display the page if the document uses UTF-8 punctuation characters, but is displayed in ISO or ASCII character sets. There are many benefits to using the Meta Content Type tag. To get the entire scoop on the Meta Content Type tags, become a paid member and subscribe to our SEO Revolution Newsletter.
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Meta Copyright
The Meta Copyright tag is used to include a copyright, trademark, patent, or other information that pertains to intellectual property.
Example of a Meta Copyright tag:

<meta name="copyright" content="Copyright 2008">

Recommendations for a Meta Copyright tag: It is not required to use a Meta Copyright tag. Please be aware that the Meta Copyright tag will not protect your site's content or your intellectual property. Consult your attorney to ensure you are protected properly.
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Meta Description
The Meta Description tag gives a brief overview of the document. The Meta Description tag is a short, plain language description of the document, usually consisting of 20-25 words or less. Search engines that support the Meta Description tag will use the information to publish on their search results page, normally displaying below the Title of your site listing.
Example of a Meta Description tag:
<META NAME="description" CONTENT="Citrus fruit wholesaler.">
Recommendations of the Meta Description tag: It is recommended to always use the Meta Description tag. Make your Meta Description as compelling as you can, as that description is often the motivating factor involved with getting your listings clicked in the search results. The Meta Description tag is particularly important if your document has very little text, is a frameset, or has extensive scripts at the top.
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Meta Designer
The Meta Designer tag is used to declare the designer of the website.
Example of a Meta Designer tag:
<META NAME="Designer" CONTENT="Art Vandaley">
Recommendations of the Meta Designer tag: The Meta Designer tag is optional to use. Usually web designers who want advertising or to catch people hijacking their designs use the Meta Designer tag. It should be understood that search engines do not support the Meta Designer tag.
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Meta Distribution
The Meta Distribution tag is used to declare the distribution of your web content. The three classifications of distribution are:
Global (the entire web)

Local (reserved for the local IP block of your site)

IU (Internal Use, not for public distribution).
Example of a Meta Distribution tag:
<META NAME="Distribution" CONTENT="Global">
Recommendations for the Meta Distribution tag: It is recommended not to use the Meta Distribution tag. If you want to have restricted distribution, use the robots.txt tag or your HTAccess file.
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Meta Expires
The Meta Expires tag is used to declare the date and time after which the web document should be considered expired.
Example of the Meta Expires tag:
<META HTTP-EQUIV="expires" CONTENT="Wed, 26 Feb 2004 08:21:57 GMT">
Recommendations for the Meta Expires tag: It is recommended not to use the Meta Expires tag. While the Meta Expires tag is good conceptually, it is impractical for search engines. Not only do search engines not read the Meta Expires tag, but according to my testing, browsers ignore it too. Are you looking to stop Google from caching your site? Even if you use the Meta Expires tag Google will cache your page. The Meta Expires tag is worthless; don't bother with it.
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Meta Generator
The Meta Generator tag is used to declare the name and version number of the publishing tool used to create the page. Tool vendors use the Meta Generator tag to assess market penetration.
Example of the Meta Generator tag:
<META NAME="Generator" CONTENT="FrontPage 4.0">
Recommendations for Meta Generator tag: It is recommended not to use the Meta Generator tag. If you have Meta Generator tags, delete them if possible. Meta Generator tags serve no useful purpose for your pages.
----------------------------
Meta Google
The Meta Google tag has several options that are exclusive for use with Google. These include:
Googlebot: noarchive - does not allow Google to display cached content

Googlebot: nosnippet - does not allow Google to display excerpted or cached content

Googlebot: noindex - similar to the robots meta element

Googlebot: nofollow - does not allow Google to pass any PageRank or link popularity to the link served.
Recommendations for the Meta Google tags: The Meta Google tags are optional to use. You generally do not need to use Meta Google tags unless you want Google to do something specific with your site. The Meta Google tag is one of the few Meta tags Google will read, index, and obey.
For more info straight from Google, see Google's Remove Page.
Also referenced: meta tags google
----------------------------
Meta Language
The Meta Language tag is used to declare the language used on the website. Webmasters who wish to declare the primary language of the web page can use the Meta Language tag.
Example of the Meta Language tag:
<META NAME="Language" CONTENT="english">
Recommendation of the Meta Language tag: It is recommended to only use the Meta Language tag for sites in non-US English languages. No testing has been done in other languages to verify that the Meta Language tag does indeed work.
----------------------------
Meta Keywords
The Meta Keywords tag is used to list keywords that define the content of your site. In addition to words from the title, document body, and other areas search engines use keywords to properly index your site. The Meta Keywords tag is typically used for synonyms and alternates of title words.
Example of the Meta Keywords tag:
<META NAME="keywords" CONTENT="oranges, lemons, limes">
Recommendations for the Meta Keywords tag: It is recommended to use the Meta Keywords tag with caution. Make sure to only use keywords that are relevant to your site. Search engines are known to penalize or blacklist your site for abuse. The Meta Keywords tag also exposes your keywords to your competitors. Five hours of keyword research can be wasted if your competitor can hijack your work within just a few minutes.
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Meta MS Smart Tags
The Meta MS Smart tags were part of a beta test of Internet Explorer and were removed due to negative press and feedback from users. In short, Microsoft would sell keyword phrases, then the Meta MS Smart Tags would allow those keywords to be highlighted on web pages that would take the user to the advertiser's site. This would mean your site could promote your competitor's site without your consent.
Example of a Meta MS Smart tags:
<META NAME="MSSmartTagsPreventParsing" CONTENT="TRUE">
Recommendations for Meta MS Smart tags: It is recommended not to use the Meta MS Smart tags. Microsoft discontinued Meta MS Smart tags technology. If you are working with an SEO firm that demands to insert these tags, quickly find a new SEO company.
----------------------------
Meta MSN (No ODP)
The Meta MSN (No ODP) tag is used for your description in the Bing search results instead of the description used in DMOZ.
Example of a Meta MSN (No ODP) tag:
<META Name="msnbot" CONTENT="NOODP">
Recommendation for Meta MSN (No ODP) tag: It is optional to use Meta MSN (No ODP) tag. If you are unhappy with the description from DMOZ, and most Webmasters are, use the Meta MSN (No ODP) tag. While this is only good for BingBot, you can sub "Robots" for "BingBOT" in the Meta MSN (No ODP) tag to be valid for all bots. As of right now, however, Bing is the only search engine using descriptions straight from DMOZ.
Note: Using the Meta MSN (No ODP) tag will not remove the DMOZ listing immediately. It can take up to four weeks.
----------------------------
Meta Pragma No Cache
The Meta Pragma No Cache tag is used to prevent visitors from seeing a cached version of a specific page. The Meta Pragma No Cache tag forces the browser to pull information from the server each time the page is viewed.
Example of the Meta Pragma No Cache tag:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
Recommendations for the Meta Pragma No Cache tag: The Meta Pragma No Cache tag has no affect on search engines and is mainly implemented with the intent of helping users. For example, if you have a site that changes on a daily basis, the Meta Pragma No Cache tag would ensure that the visitor sees the most recent version of the page.
However, since you are pulling information from the server each time a visitor views the page, the load time will be affected as well as incurring increased server activity.
Google has stated: "The http-equiv values pragma and expires are attempts at bypassing caches without having to set the HTTP headers correctly. These are probably unnecessary uses; any scenario where there is a legitimate reason to limit caching, the author is going to have enough control over the server to send the appropriate headers. In addition, the meta tags can't be considered reliable (e.g. proxies and transparent caches aren't going to honor them)."
In my opinion, it is better to set the HTTP headers correctly. To learn how to do this, view our article (must be an All Access Member of the SEO Revolution).
Note: The above also applies to the Meta Expires Tag.
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Meta Publisher:
The Meta Publisher tag is used to declare the name and version number of the publishing tool used to create the page. The Meta Publisher tag is the same as the Meta Generator tag. Tool vendors might use this tag to assess market penetration.
Example of the Meta Publisher tag:
<META NAME="Publisher" CONTENT="FrontPage 4.0">
Recommendations for the Meta Publisher tag: It is recommended not to use the Meta Publisher tag. If you have t Meta Publisher tags, delete them if possible. The Meta Publisher tag serves no purpose for your pages.
----------------------------
Meta Rating
The Meta Rating tag is used to display a content rating similar to the movie rating system (i.e. PG-13).
Example of the Meta Rating tag:
There is not a set form of this tag, nor is there any official statement from the W3C. Some sites recommend using this tag. However, these recommendations have no basis in fact as the governing body of HTML has no reference to it. According to our testing, this tag has no merit.
Recommendations for Meta Rating tag: It is recommended not to use the Meta Rating tag. The fact that there is not a set form for the Meta Rating tag suggests you would be better off acquiring a rating from the International International Content Rating Association.
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Meta Refresh
The Meta Refresh tag is used to specify a delay in seconds before the browser automatically reloads the document or URL specified.
Example of the Meta Refresh tag:
<META HTTP-EQUIV="Refresh" CONTENT="3;URL=http://www.domain.com/page.html">
Recommendations for the Meta Refresh tag: It is recommended not to use the Meta Refresh tag. Search engines can detect the use of the Meta Refresh tag and they consider it to be Spam. The penalty is either ignoring the page or banning your site completely from the index. You should use a 301 or 302 redirect instead. To get more information on how to do redirects properly, subscribe to our paid membership and check out the SEO Revolution Newsletter archive.
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Meta Reply To
The Meta Reply To tag is used to harvest email addresses. The Meta Reply To tag is a Spammers tag. The Meta Reply To tag picks up your email address, then hits you fast and hard with offers-a-plenty.
Example of a Meta Reply To tag:

<meta name="reply-to" content="your.email@address.com" />

Recommendations for the Meta Reply To tag: It is highly recommended not to use the Meta Reply To tag as it is used as a Spamming tool.
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Meta Resource Type
The Meta Resource Type tag is used to declare the resource of a page.
Example of a Meta Resource Type tag:
<META name="resource-type" content="document">
Recommendations for the Meta Resource Type tag: It is recommended not to use the Meta Resource Type tag. Use the DTD Declaration instead.
----------------------------
Meta Revisit After
The Meta Revisit After tag is used to inform search engines when to return to index your site. It has been stated that the Meta Revisit After tag will boost your site's rankings with search engines that credit fresh pages. This information is false and has no basis.
Example of the Meta Revisit After tag:

<META NAME="Revisit-After" CONTENT="30 days Days">

Recommendations for the Meta Revisit After tag: It is recommended not to use the Meta Revisit After tag. Search engines will not obey the Meta Revisit After tag and come back to index your site on their own schedule, not when you inform them.
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Meta Robots
The Meta Robots tag controls search engine robots on a per-page basis. It tells Robots they may traverse the page, but not index it.
Example of the Meta Robots tag:
<META NAME="ROBOTS" CONTENT="NOINDEX,FOLLOW">
Recommendation for the Meta Robots tag: It is recommended not to use the Meta Robots tag as the search engines often ignore it. If you need to control the search engine robots, use a robots.txt file or modify your HTAccess file instead. Many people are concerned that if a bot comes to their site through a subpage and not their homepage, the robots.txt file will not be read. This is not true. The robots.txt is read each time a good boy comes to a new domain. You can verify this through your web logs.
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Meta Set Cookie
The Meta Set Cookie tag is a cookie used to set a cookie in the user's web browser. If you use an expiration date, the cookie is considered permanent and will be saved to disk until it expires. Otherwise it will be considered valid only for the current session and will be erased upon closing the Web browser.
Example of the Meta Set Cookie tag:
<META HTTP-EQUIV="Set-Cookie" CONTENT="cookievalue=xxx;expires=Wednesday, 21-Oct-98 16:14:21 GMT; path=/">
Recommendations for the Meta Set Cookie tag: It is recommended not to use the Meta Set Cookie tag. While the Meta Set Cookie tag was used years ago to set cookies, cookies can now be set and customized very easily. If you need assistance with cookies, our programming staff can assist you for a nominal fee.
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Meta Subject
The Meta Subject tag is used to declare the subject of the web site.
Example of the Meta Subject tag:
<META NAME="Subject" CONTENT="Web Page Subject">
Recommendations of Meta Subject tag: It is recommended not to use the Meta Subject tag. No third party agents, including browsers and search engines, support the Meta Subject tag.
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Meta Title
The Meta Title tag is used to declare the title of the page. The Meta Title tag would normally have the same title as contained in the <TITLE></TITLE> tag.
Example of the Meta Title tag:
<META NAME="Title" CONTENT="Page Title Here">
Recommendation for the Meta Title tag: It is recommended to use the Meta Title tag with caution. According to our testing, Yahoo! and Bing index the Meta Title tag, but its effect on the algorithm is unknown due to inconsistent test results.
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Meta VW96.ObjectType
The Meta VW96.ObjectType is used to define the purpose of specific pages. This is based on an early version of the Dublin Core report, using a defined schema of document types such as FAQ, HOW TO, etc.
Recommendations for the Meta VW96.ObjectType tag: It is recommended not to use the Meta VW96.ObjectType tag. None of the search engine or major browsers support the Meta VW96.ObjectType tags.

Speeding up website

2010-10-28T02:30:00.000-07:00

Best Practices for Speeding Up Your Web Site

The Exceptional Performance team has identified a number of best practices for making web pages fast. The list includes 35 best practices divided into 7 categories.

Minimize HTTP Requests

tag: content

80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.

One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.

Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.

CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.

Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it's not recommended.

Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.

Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer's blog post Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.

Use a Content Delivery Network

tag: server

The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective. But where should you start?

As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.

Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This not only achieves a bigger reduction in response times, but it's easier thanks to content delivery networks.

A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.

Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, EdgeCast, or level3. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN (both 3rd party as mentioned above as well as Yahoo’s own CDN) improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.

Add an Expires or a Cache-Control Header

tag: server

There are two aspects to this rule:

For static components: implement "Never expire" policy by setting far future Expires header
For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests

Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used on all components including scripts, stylesheets, and Flash components.

Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.

Expires: Thu, 15 Apr 2010 20:00:00 GMT

If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.

ExpiresDefault "access plus 10 years"

Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js.

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user's Internet connection.

Gzip Components

tag: server

The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It's true that the end-user's bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.

Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.

Accept-Encoding: gzip, deflate

If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.

Content-Encoding: gzip

Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you're likely to see is deflate, but it's less effective and less popular.

Gzipping generally reduces the response size by about 70%. Approximately 90% of today's Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.

There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.

Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It's also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it's worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.

Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.

Put Stylesheets at the Top

tag: css

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.

Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.

The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.

The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: "Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times." Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.

Put Scripts at the Bottom

tag: javascript

The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames.

In some situations it's not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page's content, it can't be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.

An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn't support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.

Avoid CSS Expressions

tag: css

CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They were supported in Internet Explorer starting with version 5, but were deprecated starting with IE8. As an example, the background color could be set to alternate every hour using CSS expressions:

background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );

As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.

The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.

One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.

Make JavaScript and CSS External

tag: javascript, css

Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?

Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.

The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.

Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!'s front page and My Yahoo!. Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.

For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser's cache.

Reduce DNS Lookups

tag: content

The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.

DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record.

Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeout registry setting. Firefox caches DNS lookups for 1 minute, controlled by the network.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)

When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page's URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.

Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.

Minify JavaScript and CSS

tag: javascript, css

Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI Compressor. The YUI compressor can also minify CSS.

Obfuscation is an alternative optimization that can be applied to source code. It's more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.

In addition to minifying external scripts and styles, inlined <script> and <style> blocks can and should also be minified. Even if you gzip your scripts and styles, minifying them will still reduce the size by 5% or more. As the use and size of JavaScript and CSS increases, so will the savings gained by minifying your code.

Avoid Redirects

tag: content

Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:

HTTP/1.1 301 Moved Permanently
      Location: http://example.com/newuri
      Content-Type: text/html

The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control, indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.

The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.

One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite, or the DirectorySlash directive if you're using Apache handlers.

Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite.

Remove Duplicate Scripts

tag: javascript

It hurts performance to include the same JavaScript file twice in one page. This isn't as unusual as you might think. A review of the ten top U.S. web sites shows that two of them contain a duplicated script. Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts. When it does happen, duplicate scripts hurt performance by creating unnecessary HTTP requests and wasted JavaScript execution.

Unnecessary HTTP requests happen in Internet Explorer, but not in Firefox. In Internet Explorer, if an external script is included twice and is not cacheable, it generates two HTTP requests during page loading. Even if the script is cacheable, extra HTTP requests occur when the user reloads the page.

In addition to generating wasteful HTTP requests, time is wasted evaluating the script multiple times. This redundant JavaScript execution happens in both Firefox and Internet Explorer, regardless of whether the script is cacheable.

One way to avoid accidentally including the same script twice is to implement a script management module in your templating system. The typical way to include a script is to use the SCRIPT tag in your HTML page.

<script type="text/javascript" src="menu_1.0.17.js"></script>

An alternative in PHP would be to create a function called insertScript.

<?php insertScript("menu.js") ?>

In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.

Configure ETags

tag: server

Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.

HTTP/1.1 200 OK
      Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
      ETag: "10c24bc-4ab-457e1c1f"
      Content-Length: 12195

Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.

GET /i/yahoo.gif HTTP/1.1
      Host: us.yimg.com
      If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
      If-None-Match: "10c24bc-4ab-457e1c1f"
      HTTP/1.1 304 Not Modified

The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.

The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.

IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS is Filetimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS servers behind a web site.

The end result is ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn't a problem. But if you have multiple servers hosting your web site, and you're using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you're consuming greater bandwidth, and proxies aren't caching your content efficiently. Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.

If you're not taking advantage of the flexible validation model that ETags provide, it's better to just remove the ETag altogether. The Last-Modified header validates based on the component's timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:

FileETag none

Make Ajax Cacheable

tag: content

One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won't be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It's important to remember that "asynchronous" does not imply "instantaneous".

To improve performance, it's important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:

Gzip Components
Reduce DNS Lookups
Minify JavaScript
Avoid Redirects
Configure ETags

Let's look at an example. A Web 2.0 email client might use Ajax to download the user's address book for autocompletion. If the user hasn't modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn't been modified since the last download, the timestamp will be the same and the address book will be read from the browser's cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn't match the cached response, and the browser will request the updated address book entries.

Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.

Flush the Buffer Early

tag: server

When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page. During this time, the browser is idle as it waits for the data to arrive. In PHP you have the function flush(). It allows you to send your partially ready HTML response to the browser so that the browser can start fetching components while your backend is busy with the rest of the HTML page. The benefit is mainly seen on busy backends or light frontends.

A good place to consider flushing is right after the HEAD because the HTML for the head is usually easier to produce and it allows you to include any CSS and JavaScript files for the browser to start fetching in parallel while the backend is still processing.

Example:

... <!-- css, js -->
    </head>
    <?php flush(); ?>
    <body>
      ... <!-- content -->

Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.

Use GET for AJAX Requests

tag: server

The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process: sending the headers first, then sending data. So it's best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies). The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.

An interesting side affect is that POST without actually posting any data behaves like GET. Based on the HTTP specs, GET is meant for retrieving information, so it makes sense (semantically) to use GET when you're only requesting data, as opposed to sending data to be stored server-side.

Post-load Components

tag: content

You can take a closer look at your page and ask yourself: "What's absolutely required in order to render the page initially?". The rest of the content and components can wait.

JavaScript is an ideal candidate for splitting before and after the onload event. For example if you have JavaScript code and libraries that do drag and drop and animations, those can wait, because dragging elements on the page comes after the initial rendering. Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.

Tools to help you out in your effort: YUI Image Loader allows you to delay images below the fold and the YUI Get utility is an easy way to include JS and CSS on the fly. For an example in the wild take a look at Yahoo! Home Page with Firebug's Net Panel turned on.

It's good when the performance goals are inline with other web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can improve the user experience but you have to make sure the page works even without JavaScript. So after you've made sure the page works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.

Preload Components

tag: content

Preload may look like the opposite of post-load, but it actually has a different goal. By preloading components you can take advantage of the time the browser is idle and request components (like images, styles and scripts) you'll need in the future. This way when the user visits the next page, you could have most of the components already in the cache and your page will load much faster for the user.

There are actually several types of preloading:

Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components. Check google.com for an example of how a sprite image is requested onload. This sprite image is not needed on the google.com homepage, but it is needed on the consecutive search result page.
Conditional preload - based on a user action you make an educated guess where the user is headed next and preload accordingly. On search.yahoo.com you can see how some extra components are requested after you start typing in the input box.
Anticipated preload - preload in advance before launching a redesign. It often happens after a redesign that you hear: "The new site is cool, but it's slower than before". Part of the problem could be that the users were visiting your old site with a full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts that will be used by the new site

Reduce the Number of DOM Elements

tag: content

A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.

A high number of DOM elements can be a symptom that there's something that should be improved with the markup of the page without necessarily removing content. Are you using nested tables for layout purposes? Are you throwing in more <div>s only to fix layout issues? Maybe there's a better and more semantically correct way to do your markup.

A great help with layouts are the YUI CSS utilities: grids.css can help you with the overall layout, fonts.css and reset.css can help you strip away the browser's defaults formatting. This is a chance to start fresh and think about your markup, for example use <div>s only when it makes sense semantically, and not because it renders a new line.

The number of DOM elements is easy to test, just type in Firebug's console:
document.getElementsByTagName('*').length

And how many DOM elements are too many? Check other similar pages that have good markup. For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).

Split Components Across Domains

tag: content

Splitting components allows you to maximize parallel downloads. Make sure you're using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org and static2.example.org

For more information check "Maximizing Parallel Downloads in the Carpool Lane" by Tenni Theurer and Patty Chi.

Minimize the Number of iframes

tag: content

Iframes allow an HTML document to be inserted in the parent document. It's important to understand how iframes work so they can be used effectively.

<iframe> pros:

Helps with slow third-party content like badges and ads
Security sandbox
Download scripts in parallel

<iframe> cons:

Costly even if blank
Blocks page onload
Non-semantic

No 404s

tag: content

HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.

Some sites have helpful 404s "Did you mean X?", which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.

Reduce Cookie Size

tag: cookie

HTTP cookies are used for a variety of reasons such as authentication and personalization. Information about cookies is exchanged in the HTTP headers between web servers and browsers. It's important to keep the size of cookies as low as possible to minimize the impact on the user's response time.

For more information check "When the Cookie Crumbles" by Tenni Theurer and Patty Chi. The take-home of this research:

Eliminate unnecessary cookies
Keep cookie sizes as low as possible to minimize the impact on the user response time
Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected
Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time

Use Cookie-free Domains for Components

tag: cookie

When the browser makes a request for a static image and sends cookies together with the request, the server doesn't have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.

If your domain is www.example.org, you can host your static components on static.example.org. However, if you've already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.

Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the www subdomain and write the cookies to that subdomain.

Minimize DOM Access

tag: javascript

Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:

Cache references to accessed elements
Update nodes "offline" and then add them to the tree
Avoid fixing layout with JavaScript

For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.

Develop Smart Event Handlers

tag: javascript

Sometimes pages feel less responsive because of too many event handlers attached to different elements of the DOM tree which are then executed too often. That's why using event delegation is a good approach. If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of one handler for each button. Events bubble up so you'll be able to catch the event and figure out which button it originated from.

You also don't need to wait for the onload event in order to start doing something with the DOM tree. Often all you need is the element you want to access to be available in the tree. You don't have to wait for all images to be downloaded. DOMContentLoaded is the event you might consider using instead of onload, but until it's available in all browsers, you can use the YUI Event utility, which has an onAvailable method.

For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.

Choose <link> over @import

tag: css

One of the previous best practices states that CSS should be at the top in order to allow for progressive rendering.

In IE @import behaves the same as using <link> at the bottom of the page, so it's best not to use it.

Avoid Filters

tag: css

The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.

The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.

Optimize Images

tag: images

After a designer is done with creating the images for your web page, there are still some things you can try before you FTP those images to your web server.

You can check the GIFs and see if they are using a palette size corresponding to the number of colors in the image. Using imagemagick it's easy to check using
identify -verbose image.gif
When you see an image useing 4 colors and a 256 color "slots" in the palette, there is room for improvement.
Try converting GIFs to PNGs and see if there is a saving. More often than not, there is. Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past. The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don't support variable transparency either. So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations). This simple imagemagick command results in totally safe-to-use PNGs:
convert image.gif image.png
"All we are saying is: Give PiNG a Chance!"
Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:
pngcrush image.png -rem alla -reduce -brute result.png
Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize and remove comments and other useless information (such as EXIF information) from your images.
jpegtran -copy none -optimize -perfect src.jpg dest.jpg

Optimize CSS Sprites

tag: images

Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
"Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much but requires less memory for the user agent to decompress the image into a pixel map. 100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels

Don't Scale Images in HTML

tag: images

Don't use a bigger image than you need just because you can set the width and height in HTML. If you need
<img width="100" height="100" src="mycat.jpg" alt="My Cat" />
then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.

Make favicon.ico Small and Cacheable

tag: images

The favicon.ico is an image that stays in the root of your server. It's a necessary evil because even if you don't care about it the browser will still request it, so it's better not to respond with a 404 Not Found. Also since it's on the same server, cookies are sent every time it's requested. This image also interferes with the download sequence, for example in IE when you request extra components in the onload, the favicon will be downloaded before these extra components.

So to mitigate the drawbacks of having a favicon.ico make sure:

It's small, preferably under 1K.
Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision.

Imagemagick can help you create small favicons

Keep Components under 25K

tag: mobile

This restriction is related to the fact that iPhone won't cache components bigger than 25K. Note that this is the uncompressed size. This is where minification is important because gzip alone may not be sufficient.

For more information check "Performance Research, Part 5: iPhone Cacheability - Making it Stick" by Wayne Shea and Tenni Theurer.

Pack Components into a Multipart Document

tag: mobile

Packing components into a multipart document is like an email with attachments, it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive). When you use this technique, first check if the user agent supports it (iPhone does not).

Avoid Empty Image src

tag: server

Image with empty string src attribute occurs more than one will expect. It appears in two form:

straight HTML

<img src="">
JavaScript

var img = new Image();
img.src = "";

Both forms cause the same effect: browser makes another request to your server.

Internet Explorer makes a request to the directory in which the page is located.
Safari and Chrome make a request to the actual page itself.
Firefox 3 and earlier versions behave the same as Safari and Chrome, but version 3.5 addressed this issue[bug 444931] and no longer sends a request.
Opera does not do anything when an empty image src is encountered.

Why is this behavior bad?

Cripple your servers by sending a large amount of unexpected traffic, especially for pages that get millions of page views per day.
Waste server computing cycles generating a page that will never be viewed.
Possibly corrupt user data. If you are tracking state in the request, either by cookies or in another way, you have the possibility of destroying data. Even though the image request does not return an image, all of the headers are read and accepted by the browser, including all cookies. While the rest of the response is thrown away, the damage may already be done.

The root cause of this behavior is the way that URI resolution is performed in browsers. This behavior is defined in RFC 3986 - Uniform Resource Identifiers. When an empty string is encountered as a URI, it is considered a relative URI and is resolved according to the algorithm defined in section 5.2. This specific example, an empty string, is listed in section 5.4. Firefox, Safari, and Chrome are all resolving an empty string correctly per the specification, while Internet Explorer is resolving it incorrectly, apparently in line with an earlier version of the specification, RFC 2396 - Uniform Resource Identifiers (this was obsoleted by RFC 3986). So technically, the browsers are doing what they are supposed to do to resolve relative URIs. The problem is that in this context, the empty string is clearly unintentional.

HTML5 adds to the description of the tag's src attribute to instruct browsers not to make an additional request in section 4.8.2:

The src attribute must be present, and must contain a valid URL referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted. If the base URI of the element is the same as the document's address, then the src attribute's value must not be the empty string.

Hopefully, browsers will not have this problem in the future. Unfortunately, there is no such clause for <script src=""> and <link href="">. Maybe there is still time to make that adjustment to ensure browsers don't accidentally implement this behavior.

This rule was inspired by Yahoo!'s JavaScript guru Nicolas C. Zakas. For more information check out his article "Empty image src can destroy your site".

OpenSource Vs Microsoft

2010-01-23T08:45:00.001-08:00

Can the open source software movement defeat (or severely cripple) Microsoft in the marketplace?