Why is there no schema for RSS?

In my daily blog stroll a few days ago I came across a post by Mark
Pilgrim at 
	
	
http://diveintomark.org/archives/2002/08/20.html#how_liberal_is_too_libe
ral 

which implies that there are lots of broken RSS feeds on the web today.
Considering that the describing a structure for XML and ensuring that
documents conform to that structure is generally a solved problem I find
it perplexing that no schema for RSS (besides an RDF schema) exists. 

Anyone care to enlighten me? 

-- 
PITHY WORDS OF WISDOM 
Old cars never die, they just smell that way.     

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