XSL FO

Extensible Stylesheet Language Formatting Object
 

The content of any document will ultimately need to be displayed to the user.  One common method of displayed a document is to use Cascading Style Sheets (CSS).  When using CSS, no document transformations are performed.  The style sheet is simply applied to the data already in a document.

In contrast to Cascading Style Sheets XSL FO is an XML application that describes exactly the layout of text on a page.  XSLT style sheets are used to convert XML documents into XSL FO documents. 

Unfortunately, there is yet no standard web browser that supports XSL FO.  So, the XSL FO document must be processed into another form such as TeX or PDF before it can be displayed to the user.