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Another SGML Parser Question



I understand that the SGML/HTML/HText module is not well designed and it 
is going to be replaced. But if the replacement would be ready tomorrow, 
I wouldn't be asking this question. 

I was wondering if anyone could share his/her experience in modifying 
the SGML "parser" so that it generates a tree-like structure of tags 
instead of a stream of tags. More specifically, it has to do with the 
start_element() and end_element() functions in SGML.c. Currently, it 
tries to do some ad-hoc tag matching. I'm not an SGML expert but I guess 
the right way to do it is something like this:

When you see a start tag, you check the DTD to see if this tag is 
allowed in the enclosing tag. If it is allowed, then obviously you push 
this tag onto the tag-stack and go on. If it is not allowed, then the 
situation is more complex. It might be allowed inside the enclosing tag 
of the immediate enclosing tag. This way you can assume the immediate 
enclosing tag is closed and pop it off the stack and push in the new tag 
(it can be an error if explicit end tag is required for the immediate 
enclosing tag).  You might have to pop all the way up to the HTML tag if 
a tag occurs in a very wrong place. Or you can do intelligent error 
recovery to handle this. 

Is this a reasonable way to parse SGML? Has anyone done something like 
this?

-Kim