[xml] DTD ID attribute

["Daine Mamacos" <scuzzy reverseorder net>]

I was wondering about this DTD ID attribute.
In the DTD if you specify something like:
<!DOCTYPE tree [
<!ATTLIST content content_id ID #IMPLIED>
]>
the content_id works as being purly numerical.
If you don't prefix this with a letter (NCName) you can still fetch the
element  by fetching it by it's id.
however, if you try validate the document, and it has these id's as purly
numerical, it fails.
There is very little documentation clarifying whether this field can be
numeric only or not. I've searched a lot of WC3 and can't find much about it.
Is it a bug that one can still search on this id dispite it not being
valid(NCName)?

Any help would be appreciated.
Many Thanks
Daine Mamacos.

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