xu_text_2--benja: Separate xu text from xu media

XML-based formats (as well as e.g. YAML or RDF) know plain-text strings-- sequences of characters. Images or audio units cannot be embedded in these sequences. These formats refer to images by URIs, but not to text, which they include directly. We want to enhance such formats with Xanalogical text.

Giving Xanalogical identities to the character content in an XML file seems like a much less intrusive change than using an enfilade format which can include e.g. audio as well as characters, so that you could say <tag> 10000 audio units </tag>.