Cross-Browser Compatibility

Web browsers implement HTML coding differently and some browsers expand the HTML code with extensions of their own that are not even available to other browsers. Many web page developers code for only one browser, with no regard for how their pages will display in other browsers or on other computer platforms. Adapting code from the source code of someone else's pages may also lead to code that is not valid across browsers.

The following discussion itemizes components and their features that inhibit consistent web page displays and performance. The steps you can take to minimize the effect of feature inconsistencies are addressed at the conclusion of this discussion.

Issues related to consistent web page display and performance

Computers

Resolution

A user's machine sets constraints on the size of the page as it is displayed on the screen. A screen resolution of 640 x 480 will display less material than will a resolution of 800 x 600. If you design a page set for a resolution of 800 x 600 and the user is viewing the page with a monitor setting of 640 x 480, the user will be required to scroll to see some the information that is instantly viewable with an 800 x 600 setting.

Color Capacity

The number of colors available for a web page display are controlled by the computer, by its inherent limitations and by the options available for the user to set. Users limited to 256 colors by the computer configuration will not properly be able to see additional colors coded to be displayed. The computer will dither the colors it has available in an attempt to render the intended colors. The results are often undesirable.

Platforms

The operating system used by a computer affects how colors are rendered on the screen. There are only  216 colors that will display consistently on both a PC and a MacIntosh computer. Other colors not in that 216 color palette are interpreted differently, again with frequently undesirable results.

Communications

The speed of data transfer between a user's machine and the addressed  web server affects how long it takes a requested page to be displayed on the user's screen. Large graphics can take so long to download to a screen that the user may move on to another site before the image is completely rendered on screen.

Browsers

Version

Not only do you need to be concerned about compatibility between different browser makers, but also between different versions of the same browser. New versions of browsers add features that are not available to older versions of the same browser.

Interpretation of Code

Browsers vary in how they  implement standard code. Some browsers even create their own codes which are not available to other browsers. Scripting languages, such as JavaScript, are implemented differently between Netscape and Internet Explorer, for example. Internet Explorer also has proprietary scripts.

HTML is the fundemental language for web-based page display. HTML also changes with each new version. Some browser versions are not consistently compatible with particular tags in various versions of HTML or their latest extenstions, Cascading Style Sheets (CSS) and Dynamic HTML (DHTML). Older browsers do not support tables or frames, for example. Another example is browsers that also may differ in their interpretation of the attributes of a tag, or may have created an attribute for a tag that is not available to other browsers.

Default Display Options

In most cases, if the browser does not support a tag, it will ignore it. The danger is in the subsequent appearance of the displayed page. If the browser does not support changing the font
color and the default does not contrast enough with the background, or if your
animated gif does not work. All of these features need to be taken into account.


The font, font size and background color displayed on a user screen can be altered, as well as other settings, by the user. Some users may choose to default to the settings coded into the web page. Some users may never adjust their display settings and let the browser defaults determine the page appearance. Browser defaults vary among browsers.

Tag Forgiveness

Guidelines for Developing Web Pages that Display Consistently Across Web Browsers

Coding

Using standard HTML code is the only way to ensure that your pages will display correctly in all browsers that support the version of HTML you are using.

Sites that are accessible in Lynx are, in general, accessible by all software,
including that for the visually impaired

Testing

HTML Checking


• Install several different browsers on a test machine to confirm how various browsers display web pages.



• User Software
  http://www.macromedia.com/software/dreamweaver/Dreamweaver - Dreamweaver
  
  - checks HTML code for targeted browsers
  - saves DHTML that is developed in HTML 4, in both 4.0 and 3.0 (3.2?) also
  - scripts for cross-browser compatibility
  - detects visitor browser and sends appropriate coding format

• Sites providing browser compatibility checking with a number of different browsers
  http://www.websitegarage.com - Web Site Garage
  http://www.cast.org/bobby - Bobby

Page Download-time Checking


• Homesite


• FrontPage 98

IHS Cross-Browser Compatibility Standards

• code a background color in the body tag (avoid defaulting to the browser default)


• baseline:  IE and NS 3. 


• design for 640 x 480 screen resolution