Monday 19th of March 2018 08:01:42 AM

CSS Style Guide

XHTML: Guidelines

All developers are familiar with HTML, the web’s original markup language. But the W3C currently recommends using XHTML instead. This hybrid language looks and works much like HTML but is based on XML, the web’s “super” markup language.

The Library has standardized on XHTML 1.0 Transitional, a version of XHTML that works well in both old and new browsers, and that accommodates the needs of older browsers (such as Netscape Navigator 4 and Internet Explorer 4) that are used by a significant portion of the NYPL audience.

Rules of XHTML

Converting from traditional HTML to XHTML 1.0 Transitional is easy, as long as you work carefully and observe the following rules:

1. Open with the proper DOCTYPE & Namespace

XHTML documents must begin with tags that tell the browser how to interpret them. All library web pages must begin with the following DOCTYPE declaration:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
" ">

The declaration above should be typed (or cut and pasted) into the very top of every XHTML document, before any other code or markup. View Source on this page to familiarize yourself with the proper placement of this DOCTYPE.

The XHTML 1.0 Transitional DOCTYPE must be followed by this XHTML namespace declaration:

<html xmlns="" xml:lang="en" lang="en">

Once again, View Source to familiarize yourself with the proper placement of the namespace declaration.

Note: many XHTML pages begin with an optional XML prologue (<?xml>) that precedes the DOCTYPE and namespace declarations. Unfortunately, this XML prologue causes problems in many browsers and must be omitted from NYPL web pages.

One of the main purposes of the prologue is to specify character encoding within your document. If you’re working on an international site and your page will include non–ASCII characters, you can probably get by with a simple meta tag such as:

<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
2. Write all tags in lowercase

Unlike HTML, XML is case–sensitive. All XHTML tags and attributes must be typed in lowercase, or your document will not validate. (Validation ensures that your pages are error-free. See the section on validation if you are unfamiliar with this subject.)

In order to "translate" an older document to XHTML, the following markup ...

<TITLE>New York Public Library</TITLE>

... would be recast thusly:

<title>New York Public Library</title>

Likewise, <P> becomes <p>, <BODY> becomes <body>, and so on.

3. Quote all attribute values

this page.</A>  (I stuck a hidden anchor tag there:&lt;ANAME="top"&gt; &lt;/a&gt;)
Use anchors to improve navigability, but remember that multiplelinked pages will download quicker than one huge page requiring lots ofanchor tags!Here's a link to the top of this page.  I stucka hidden anchor tag there: <A NAME="top"> </A>  Use anchorsto improve navigability, but remember that multiple linked pages will downloadquicker than one huge page with lots of anchor tags! 

In HTML, you needn’t put quotation marks around attribute values. In XHTML, they must be quoted, e.g., height="55", not height=55.

4. Close all tags

In HTML, you have the option to open many tags such as <p> and <li> without closing them:

<p>This would be invalid XHTML.
<p>I forgot to close my Paragraph tags!

In XHTML, every tag that opens must close:

<p>This is valid XHTML.</p>
<p>I close my tags after opening them.</p>
5. Close “empty” tags, too

In XHTML, even “empty” tags such as <br> and <img> must close themselves by including a forward slash /> at the very end of the tag:

<br />
<img src="library.gif" />

Note the slash /> at the very end. Note also that a single blank space precedes the slash to avoid confusing older browsers that were released prior to the XHTML standard.

Important: To remain valid and accessible, the image tag in the second example would also have to include an “alt” attribute, and an optional “title” attribute wouldn’t hurt:

<img src="library.gif" alt="New York Public Library" title="A view of the main Library at 42nd Street and Fifth Avenue, Manhattan." />
« XHTML Section Index | XHTML Benefits »

rectangle's bottom to align with the bottom of the image, andthe right edge to the right edge of the image. The value of0 for left keeps the left edgeof the clipping rectangle against the left edge of the image, but the10px for top moves the top edgeof the clipping rectangle downward 10 pixels. This will cause the top10 pixels of the image to become effectively invisible.

clip can be applied to any element. Thus, youcould display only the top left corner of a paragraph using somethingpadding-left, width , padding-right, border-right, and margin-right. These are illustrated in Figure 8-9. The values of these seven properties must equal the value of width for an element's parent.

Figure 8-9

Figure 8-9. The "seven properties" of horizontal formatting

Only three of these seven properties can be set to auto: the width of the element's content, and the left and right margins. The left and overflow were declared to bevisible.

If the overflow is set tohidden, the element's content is clipped,but no mechanism should be provided to make the content accessible tothe user. Consider the following styles:

DIV#sidebar {position: absolute; top: 0; left: 0; width: 15%; height: 7em;overflow: hidden;}
interpret them as if the decimal wasn't there, which would lead them to think the preceding value is actually rgb(255%,40%,986%). In that case, assuming the user agent behaves correctly, the out-of-range values will be "clipped" to the nearest legal value -- in this case, 100%. Thus, a user agent which ignores the decimal points should act as if the declared value is rgb(100%,40%,100%). Whether it does so is, of course, another story altogether. Also,
negative values aren't allowed, so any value set to be less than