Re: [xml-dev] newline/form feed valid as attribute value?

[David Carlisle <davidc@nag.co.uk>]

On 02/07/2012 21:43, Dan Shelton wrote:
> On 2 July 2012 22:17, Michael Kay <mike@saxonica.com> wrote:
>> It's theoretically impossible to write an XML parser using regular
>> expressions alone, because XML is not a regular language.
>
> So what's wrong with the following regex pattern? It was passed around
> by Roland Mainz in David Korn's ksh93 mailing list a few weeks ago and
> is used as a *core* (there's more prep and postprocess code, but the
> parsing alone is done by repeatedly applying the regex to a character
> stream) for a xml fragment parser (brackets not postfixed with ?:
> capture data and are stored in the 2D array .sh.match):
> ---------------
> dummy="${xmltext//~(Ex-p)(?:
> 	(<!--.+-->)+?|	# xml comments
> 	(<[:_[:alnum:]-]+
> 		(?: # attributes
> 			[[:space:]]+
> 			(?: # four different types of name=value syntax
> 				(?:[:_[:alnum:]-]+=[^\"\'[:space:]]+?)|	#x='foo=bar huz=123'
> 				(?:[:_[:alnum:]-]+=\"[^\"]*?\")|		#x='foo="ba=r o" huz=123'
> 				(?:[:_[:alnum:]-]+=\'[^\']*?\')|		#x="foox huz=123"
> 				(?:[:_[:alnum:]-]+)				#x="foox huz=123"
> 			)
> 		)*
> 		[[:space:]]*
> 		\/?	# start tags which are end tags, too (like <foo\/>)
> 	>)+?|				# xml start tags
> 	(<\/[:_[:alnum:]-]+>)+?|	# xml end tags
> 	([^><]+)			# xml text
> 	)/D}"
> ---------------

The comment regexp also does not match the XML 9or HTML) syntax. the .+ 
in the middle means it won't accept <!----> which is a well formed XML 
comment and it will accept <!-----> which is not a well formed comment.

The regexp for element and attribute names does not match that of xml 
(4th edition) xml (5th edition) or html. the details vary but in all 
cases the set of characters allowed for the first letter is more 
restricted than the set of characters allowed for following letters. 
<a1> is well formed but <1a> is not.

David

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