> Does anyone know of an XML editor that allows valid values to be
> obtained from an external document?
I think both ADEPT and Author/Editor can do this if you write a script
for them (they both have their own programming language which can be
used for customisation), but both languages are pretty arcane, and
this level of customisation is something the manufacturer normally
does for a big client as part of the project installation (although
there are consultants who will write this kind of thing as well).
It should be fairly easy for a good elisp hacker to write something
for Emacs/psgml that would perform some kind of extrinsic validation
on a value, but I don't know if anyone has actually done this.
> I **assume** that the validating editors use valid values that are
> explicitly included in the DTD. But, what if the valid values are
> huge, for example the country codes or geoloc codes? It'd be nice to
Right. Including the ISO 3166 two-letter country codes in a DTD is
easy, but SGML systems have no method for specifying machine-performed
range checks, so validating latitude and longitude (a
commonly-requested example) has to be specified elsewhere,
programmatically. An XSL or DSSSL stylesheet, however, could specify
an external action to perform this.
> Does such an editor exist, is someone building such an editor, or does
> the spec allow for this to occur so that it will be done in a
> consistent manner across multiple implementations?
Nope. It's everyone for themselves right now. Most of the available
editors have only just crawled out from under the stone, in
user-interface terms, so I suspect this kind of facility is still a
fair way off: many editor-makers would expect users to use database or
spreadsheet front-ends for this kind of validation.