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="http://www.w3.org/1999/xhtml" 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>
<body>, and so on.
3. Quote all attribute values
In HTML, you needn’t put quotation marks around attribute values. In XHTML, they must be quoted, e.g.,