DTDs, Validation, Namespaces

XML Declaration

This is the first line of an XML document: <?xml version="1.0" ?> It is optional in XHTML.

DOCTYPE

The Document Type Definition (DOCTYPE) declaraction tells the browser which XHTML 1.0 version you are using: Strict, Transitional, and Frameset. The three DOCTYPEs only differ at two points.

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

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

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

Requirements of XHTML:

1. A DOCTYPE declaration is required and the XML declaration is optional.

2. Element and attribute names must be in lowercase.

3. Elements must either have an end tag or end in />.

4. Attribute values must be quoted.

5. XHTML does not permit attribute minimization -- e.g. for a checkbox in HTML that is initially checked, one would write <input type="checkbox" checked>. In XHTML, one must write <input type="checkbox" checked="checked">

6.. Documents must be well-formed; that is, they must conform to the syntax rules of the language: contain a root element <html>, tags must be nested, all attributes must have a value.

7. One must use the id attribute for naming <form>, <frame>, and <map>.

Validators

http://validator.w3.org - XHTML

http://jigsaw.w3.org/css-validator/ - CSS - do XHTML validation first

Alternatives to Deprecated Tags and Other Things Not in XHTML Strict

XHTML strict does not permit the use of a number of tags and attributes that were used in HTML. The table below attempts to provide an alternative:

<font> tag CSS properties of font-family, font-size, color
<center> tag <span style="text:align:center"> ...</span> -- seems to center non-text as well
<u> tag

CSS applied to <span> or other tag:

text-decoration:underline
bgcolor, background, text attributes of <body> tag

CSS properties applied to body tag:

body {background-color:value;
background-image: value;
color: value}
alink, vlink, and link attributes of <body> tag

CSS properties:

a:alink {color: value}
a:link {color: value}
v:link {color: value}
target attribute of <a> tag target is in the frameset dtd but not in strict so its use with frames would be OK
border, hspace, and vspace attributes of <img>

CSS border properties applied to img tag

border property (one possible value is none)
margin-top, margin-right, margin-bottom, and margin-left properties (one possible value is a length measurement in pixels such as 15px
align, bgcolor, background attributes of <table> tag

CSS properties applied to <table> tag:

table {background-color:value;
background-image: value;}
bgcolor, background, width attributes of <td> tag

CSS properties of background-color, background-image, and width applied to particular <td> in question

For column widths, since the width of a column is constant across the rows, one can either apply this to a single row, or create a class for each column and define the width for that class.

Revised: April 20, 2010. Comments to William Pegram, bill@billpegram.com