Appendix E. HTML/XHTML DTD Support

With so many flavors of HTML 4 and XHTML specified by the W3C, it’s not always easy to remember which elements and attributes are safe (i.e., validate without error) for a particular Document Type Definition that you specify in the <!DOCTYPE> header of your file. The large table in this appendix lists a union of all elements and attributes for the most common HTML 4.01 and XHTML 1.0 DTDs from the W3C. If an attribute is required for validation, it is marked “req’d”.

The five DTDs referenced in the table can be specified at the top of your documents as follows:

HTML 4.01 Transitional 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
HTML 4.01 Strict 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
    "http://www.w3.org/TR/html4/strict.dtd">
XHTML 1.0 Transitional 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
XHTML 1.0 Frameset 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
XHTML 1.0 Strict 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

See the discussion of the <!DOCTYPE> element in Chapter 1 about the implications of DTD specifications in the most recent browsers.

Element/Attributes

HTML 4.01 Transitional

HTML 4.01 Strict

XHTML 1.0 Transitional

XHTML 1.0 Frameset

XHTML 1.0 Strict

a

yes ...

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