xml-dev - XSchema: unparsed entities

[rbourret@dvs1.informatik.tu-darmstadt.de (Ron Bourret)]

At the risk of becoming flame bait, I'd like to ask again why we removed 
unparsed entities from XSchema.

On the one hand, unparsed entities exist for purely physical reasons -- you 
can't easily stored binary data in a text (XML) file -- and therefore don't pass 
our XSchema-describes-logical-structures-only test.

On the other hand, an unparsed entity is a very close cousin to a PCDATA-only 
Element with a NOTATION attribute.  In both cases, a separate application 
processes the data and the only real difference seems to be whether the XML 
parser first parses that data; that the unparsed entity data is stored 
separately is really a red herring.  Thus, the unparsed entity becomes a special 
type of element (logical structure) for holding unparseable data.

One other difference I'd like to point out is that, with the exception of the 
"escape character" entities (lt, gt, amp, quot, and apos), I don't think you can 
construct an XML file with parsed entities that you cannot construct without 
them.  This is not true of unparsed entities.  Not only would an UnparsedEntity 
element rectify this problem, it would also solve the validation problem pointed 
out by John Cowan with respect to ENTITY attributes: we can't validate their 
value without unparsed entity declarations.

-- Ron Bourret

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