1) if the citation is not a one-shot thing, I would recommend creating an
external list of sources and making a reference into that list (rather than
hard-coding it into the tag)
2) either way, rather than using a #:source attribute within `epigraph`, you
could make a `source` subtag within,
I am interested in creating a tag function that could accept as one of its
attributes, a complete txexpr; this txexpr could contain a citation for the
tagged material, or could offer a translation into another language. For
instance, providing source and language information for an epigraph:
