XHTML modules provide means for subsetting and extending XHTML. XHTML modules are used for creating new flavors of XHTML, such as XHTML Basic for mobile devices.
Core modules are
* Structure (html, head, body, title...)
* Text (h1, h2, h3... p, pre...)
* Hypertext (a)
* List (ul, li...)
Other modules include applet, image, forms and basic forms.