I was in beginning html class all day

xml is more of a database language for the net than anything like mark-up language in its current form. Even with the existense of xsl, it's main function is still to be used in conjunction with a schema language.
 
The fact is that xml is used more and more nowadays because of its inherent ability to check the validity of the data being transmitted (i.e. any form sent is automatically checked using the schema to see whether each and every piece of data is nested correctly according to the xml code, and so less unusable information is passed around.)