It
It
http://www.it.uc3m.es/jaf/html2xhtml
Ivobrugge
Cursusweb : online cursussen - leer html,asp,xhtml,css,javascript,dhtml,asp.net - handleiding en tutorial op het net
http://www.ivobrugge.be/cursusweb/index.asp
Webstandards
The web standards project is a grassroots coalition fighting for standards which ensure simple, affordable access to web technologies for all.
http://www.webstandards.org/learn/articles/askw3c/oct2003
W3schools
Free html xhtml css javascript jquery xml dom xsl xslt rss ajax asp .net php sql tutorials, references, examples for web building.
http://www.w3schools.com/xhtml
XHTML 1.0 (engels)
XHTML 1.0 (engels)
http://www.w3.org/tr/xhtml1/
XHTML 1.1 (engels)
XHTML 1.1 (engels)
http://www.w3.org/tr/xhtml11/