id uniqueness test for encryption.xml

[rdeltour]

From mgarr...@gmail.com on September 20, 2013 17:43:04

Since the xml sec schemas are not maintained in the epub core specs anymore, moving issue 244 over here.

Id attributes in the encryption file do not report uniqueness errors.

As noted in the RNC:

# (1) ds_IdType
#
# This is defined as xsd:NCName.  One might want to use xsd:ID 
# instead, but jing is likely to report an error.  This is because 
# of the compatibility requirement for the ID/IDREF/IDREFS feature, 
# which is specified in the OASIS committee specification 
# "RELAX NG DTD Compatibility" (December 2001).

It would be useful to add a schematron check to verify IDs in these files.

Original issue: http://code.google.com/p/epubcheck/issues/detail?id=307

[mattgarrish]

I haven't tried to scour the xmldsig-core schema, but the reason for using NCName is that if the schema is permissive enough in its content models, you can end up with the same element with the same attribute, but where the processor cannot determine the type. James Clark has written about the issue here: http://blog.jclark.com/2009/01/relax-ng-and-xmlid.html

To check uniqueness of id attributes, we need a secondary check in schematron, similar to how opf validation uses NCName for @id and then the id-unique.sch schema validates the IDs. I believe that schema could be reused here.

[rdeltour]

This looks rather straightforward to implement; we even have an existing generic schematron to check such IDs.

Tentatively adding this to 4.2.0 so that we can close this one.