Use InDesign GREP to Identify and Modify XML Tagged Text?

Apart from various other mistakes (see the other posts ), this one is the most important:

GREP inside InDesign only works on plain text inside InDesign.

That means you cannot search for 'xml tag names' with GREP, just like you cannot search for a paragraph style name ("Heading \d") or a swatch name ("\[Paper\]"). GREP also cannot find the individual digits in an automatic page number code, or any text inside variables.

You are thinking way out of the box. It seems all you want to do is apply special formatting to an XML element called "saleprice". Why not use the regular functions for that?

TLDR: No.

More details:

I saw the following information under the XML Character Classes section on the InDesign GREP Help page: "\i, \I, \c and \C shorthand XML name character classes"

Oh, this is Jongware's page: http://www.jongware.com/idgrephelp.html.

Does this mean it is possible to set up a GREP style that identifies any text that is tagged with a specific XML name? If so, can someone explain how this would work - none of my GREP styles have worked so far.

No, it doens't mean that. That table is a survey of whether InDesign's GREP implementation supports regular expression features, and adjacent to that feature it says "No."

Furthermore, I don't believe that feature would do what you think it does. See http://www.regular-expressions.info/xmlcharclass.html. They allow you to match characters that are valid in tags, but not a specific tag.

For InDesign regexp reference, I would stick with Metacharacters for searching.

In the future, if you're citing a non-Adobe reference, it's probably good to be more clear about that. At first I thought you were discussing Adobe's web page on the topic and got fairly confused.