I suppose it would also make sense to have the same subtypes as for work-author authorship (so written at, composed at, (translated) lyrics written at, (translated) libretto written at), as well as the "additional" flag.

Example: http://musicbrainz.org/work/1b0da3fa-7bb9-44e3-be87-ce7a0ea6e756
There the writing location was listed in the booklet.