Settings are validated on read, not only on write: several go straight onto
foliate's renderer as custom-element attributes, where a bad value wedges the
layout silently rather than throwing. Unknown keys are stripped and missing
ones filled from the defaults, so settings added later do not invalidate what
a reader already has stored.
The stylesheet is built as foliate's [before, after] pair. The paginator
prepends the first to the section's <head> and appends the second, so the
book's own CSS overrides the first and loses to the second. Typography goes
in the first — a book that styles its own headings still gets to, and font
size lands on <html> without !important so rem/em headings scale rather than
being flattened. Colour goes in the second, because most EPUBs set a body
background and would otherwise leave the page white against a dark UI.
Font choices are reused from the app theme's FONT_STACKS rather than
duplicated, so the reader cannot drift from the rest of the UI.
Rename the ambient declaration to foliate-js.d.ts: as foliate.d.ts beside
foliate.ts, TypeScript takes it for that file's emitted declaration, drops it
from the program, and every $foliate import fails with TS2307.
patrick
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