Add manifest/resource/@roll attribute

[mhosken]

A DBL bundle contains a number of key files. For example in a text context, there are the styles.xml, versification.lds and language LDML files. Currently these files are identified purely by name and location. Moving to a manifest driven structure, it would be helpful if the mapping between a file and its role were not via an informal naming scheme. Instead, files with a particular roll would be so identified in the manifest.

The value of the roll attribute would be from a list of reserved keywords. For example:

commonManifestResourceAtts &= {
    attribute roll { "styles" | "versification" | "ldml" }
}

In addition, I would add a constraint that one and only one resource must contain a roll attribute of each of the values listed. That is there must be a "ldml" resource and a "styles" resource, etc. But how strict you make that requirement (how necessary each resource is) is up to you. I don't think such a constraint is representable in RelaxNG (although it is in schematron).

I'm afraid I don't know enough about other DBL module types (audio, braille, etc.) to be able to suggest rolls useful in those modules, but I'm sure you can add what is necessary.