Markdown file converted inside veiled assets directory.
Guise Mummy seems to be converting an _assets/foo.md file to HTML as if it were a source document, when _assets is a veiled directory.
Upon reflection it is apparently why Guise Mummy is doing this: the directory is hid from navigation, but that's it. We need to decide if "veiled" includes the semantics of "untouched" or "leave as is". Or do we need another designation for unmodified source files?
It turns out that a separate designation for "assets", implemented in solves this problem very nicely. So rather than using a veiled directory _assets/foo.md, the recommendation will be to use an assets directory $assets/foo.md from instead.