Compile-time [part=] coverage over a document root's render closure
(DESIGN.md §9).
Every part emitted by a routed resource's view — including everything it
transitively render()s — must match a [part=...] rule in the resource's
effective stylesheets. The extractor is a comment- and string-aware SCANNER,
not a CSS engine: [part="x"], [part='x'], and [part=x] are matched
literally.
Also enforced here:
@importanywhere in a declared sheet is a compile error — thestylesheetslist is the sole import order.- Every declared sheet must exist as a readable file at compile time (paths resolve relative to the compiling project's root).