Entity and Element Addressing

Entity and Element Addressing

| 4.3 SGML Reference Types
| SGML HREFs use standard SGML Element and Entity addressing mechanisms. 
| If the reference type is ENTITY, then the HREF must be an entity name 
| which references an external entity. 

"External entity" is defined in XML 1.0, s.v. 4.2.2, which should
be referred to here (some readers will become confused and wonder
whether they can use this mechanism to refer to é).

I note from XML 1.0, s.v. 2.2, that in a well formed XML document,
for each entity reference, the entity name must be declared in
the doctype declaration (at that point, reference might be made
to 2.9, in which the concept of internal and external subsets
is introduced).  S.v. 4.2.2, the system identifier
must be a URL (should the sentence following the Validity
Check following production 71 start "The SystemLiteral"?).  It might
be worth while pointing out that in xmllink, addressing by entity
means addressing by URL using entities for indirection.  Is
ENTITIES allowed? 

| If the reference type is ELEMENT, 
| then the HREF must be the value of a unique identifier attribute within 

"Unique identifier attribute" isn't language I can find in XML 1.0.
Is "ID value" intended?  What of ELEMENTS, in the plural?  (In other
words, is this really IDREF/IDREFS?)

| the current document. If the reference type is SGML, then the HREF must 
| contain an entity name interpreted as with ENTITY, followed by the 
| character "#", followed by the value of a unique identifier attribute 
| within the document referenced by the leading entity name.

What happens when the system identifier for the entity already
contains a #?  What is the force of "leading" in "leading entity name"?

    Terry Allen    Fujitsu Software Corp.    tallen@fsc.fujitsu.com
"In going on with these experiments, how many pretty systems do we build,
 which we soon find outselves obliged to destroy?" - Benjamin Franklin
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