I'm actually working on something similar, and I've settled with using a JSON file on the server that describes what type of elements/attributes are allowed.

When a user uploads a XML file, it can be compared to the data file on the server through a script, and elements or attributes with improper syntax can be rejected.

As far as a standard way of doing this, I'm not aware of any, though this method has been working quite well for me so far.

Here's what my test JSON object looks like:

XMLTemplate = { xml : '<?xml version="1.0" encoding="UTF-8" ?>', doctype : '<!DOCTYPE xml PUBLIC>', children : [{ name : "ROOT", description : "All xml documents have a root tag", children : [{ name : "GROUP", description : "Groups contain products, as well as some fields", attributes : [{ name : "TYPE", description : "What type of product" },{ name : "DESCRIPTION", description : "Group Description" }], children : [{ name : "TITLE", description : "Title of the group" },{ name : "DESCRIPTION", description : "Group description", attributes : [{ name : "SOMETHINGELSE", description : "some other attribute I don't know" },{ name : "WIDTH", description : "" }] },{ name : "PRODUCT", description : "Products contain some stuffs", attributes : [{ name : "TYPE", description : "type of product" },{ name : "SOMETHINGELSE", description : "some other attribute I don't know" }], }] }] }] }