xml:space

[David Megginson]

Michael J. Suzio writes:

 > What I wonder is, how does SAX decide what is ignorable
 > whitespace and what is significant?  I'm not clear on how that
 > works, and the role xml:space plays in defining that.  
 > Ignoring whitespace is one of the most tedious things I keep doing
 > in my XML parsing apps, I'd prefer to have to explicitly *work* to
 > keep whitespace.

SAX itself is not a program, but its interface allows DTD-driven
parsers to make the distinction described in clause 2.10 (AElfred
takes advantage of the distinction):

  2.10 White Space Handling

   In editing XML documents, it is often convenient to use "white space"
   (spaces, tabs, and blank lines, denoted by the nonterminal S in this
   specification) to set apart the markup for greater readability. Such
   white space is typically not intended for inclusion in the delivered
   version of the document. On the other hand, "significant" white space
   that should be preserved in the delivered version is common, for
   example in poetry and source code.
           
   An XML processor must always pass all characters in a document that
   are not markup through to the application. A validating XML processor
   must also inform the application which of these characters constitute
   white space appearing in element content.

Note that this has nothing to do with the `xml:space' attribute -- it
is your application, rather than the XML parser, that is allowed to
act on that one.

 > What I don't understand is, given something like this in a DTD:
 > 
 > <!ELEMENT QUOTE (SOURCE?|LINE+|KEY+)>
 > 
 > Why wouldn't *any* character data located within
 > <QUOTE></QUOTE> (and not inside one of it's child
 > elements) be ignorable?  I'd expect a parser seeing this:
 > <QUOTE>
 >  <SOURCE href="http://www.quotesrus.com/">
 >  <LINE>This is line 1 of the quote</LINE>
 > </QUOTE>
 > 
 > To ignore those carriage returns and extraneous spaces within the
 > QUOTE element, and just give me the SOURCE and LINE elements and
 > their content.

Absolutely correct.  If your XML parser is DTD-driven (as AElfred is),
it should somehow flag the carriage returns and leading spaces in your
example as ignorable.  It is a major pain having to deal with this
kind of thing yourself, if your parser is not DTD-aware.


All the best,


David

-- 
David Megginson                 ak117 at freenet.carleton.ca
Microstar Software Ltd.         dmeggins at microstar.com
      http://home.sprynet.com/sprynet/dmeggins/

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