Monday 19th of March 2018 08:00:49 AM

CSS Style Guide

XHTML: Accessibility Tips

The library is committed to serving the entire public, and that means striving to ensure that all pages of our site are accessible to the greatest possible number of people and devices (including audio browsers, Braille readers, and other specialized browsing environments).

In addition, accessibility is now U.S. law for all government and publicly funded sites.

Education and Compliance

The following links can help you develop pages that comply with accessibility laws and guidelines:

WAI Accessibility Guidelines
These guidelines offer compliance tips, and outline various levels of compliance.
Bobby Accessibility Validator
The Center for Applied Special Technology has created this online tool that analyzes web page accessibility based on the W3C guidelines.

Accessibility and Web Standards

In a perfect world, the library’s website would be authored in XHTML 1.0 Strict, using absolutely no deprecated HTML “design” elements. Visual design would be handled via Cascading Style Sheets exclusively.

This strict separation of structure (XHTML) from style (CSS) would enable us to comply with the W3C's Priority One rating for User Agent Accessibility Guidelines 1.0, and would also vastly simplify the design, development, and maintenance of our site.

With such an approach, our site could look great in a standards–compliant browser, and yet remain accessible to virtually any known browser or Internet device.

The Bad News

Unfortunately, many web browsers used by our audience are not sufficiently CSS-compliant - over one third still use some version of Netscape 4.x. Happily, NYPL has upgraded our onsite PCs to Internet Explorer 5.5.

The Transitional Solution

In order to design sites that achieve at least a minimum of accessibility and that work well in Netscape 4, our pages must:

In addition, all XHTML and Style Sheets must validate, a simple process described on the very next page. »

« XHTML Section Index | XHTML Validation »

Figure 6-36

Figure 6-36. Centering a single background image

This positioning is all done using background-position, of course, but there are a whole lot of ways to supply values for this property. First off, there are the keywords top, bottom , left, right, and center. Usually, these appear in pairs, but (as Figure 6-36} shows) this is not always true. Then there are length values, such as 50px or 2cm , and finally,

You cannot, however, mix keywords with othervalues. Thus, top 75% is notvalid. If you use a keyword, you're stuck using only keywords,but percentages and lengths can be mixed together.

Not only that, but if you're using lengths or percentages, youcan give negative values, thus pushing the image out of the element,to some degree. Consider the example with the very large yin-yangsymbol for a background. At one point, we centered it, but what if weonly want part of it visible in the top left corner of the containingnone is the value you seek.none will cause the user agent to refrain fromputting anything where the bullet would ordinarily be, although itdoes not interrupt the counting in ordered lists. Thus, the followingmarkup would have the result shown in Figure 7-80:

OL LI {list-style-type: decimal;} {list-style-type: none;}<OL><LI>Item the first