HTML / XHTML DTD

XHTML 1.1: http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd
XHTML 1.0 STRICT: http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd
XHTML 1.0 TRANSITIONAL: http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd
XHTML 1.0 FRAMESET: http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd
XHTML Basic 1.0: http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd
HTML 4.01 STRICT: http://www.w3.org/TR/html4/strict.dtd
HTML 4.01 TRANSITIONAL: http://www.w3.org/TR/html4/loose.dtd
HTML 4.01 FRAMESET: http://www.w3.org/TR/html4/frameset.dtd