The definition of ElementDefinition.short says:

A concise definition that is shown in the generated XML format that summarizes profiles (used throughout the specification).

Is this mean to be describing XHTML snippets? Or just plain strings? It would be best not to cram XML or XHTML into a FHIR string in this field, and the examples in the spec itself just use plain strings. So I think this description should instead read something like:

"A concise description of what this element means (e.g. for use in auto-generated summaries)".