fetchRemoteResources

Fetches chapter's remote resources through EpubSettings.resourceFetcher, and returns once each has landed or failed (#38). Only https URLs are fetched (EPUB Reading Systems 3.3, 3.3). Returns at once without a fetcher, or for a chapter the book does not have.

Layout never waits for the network on its own. An image whose width and height the markup gives keeps that room, and its page paints the picture once its bytes land, which remoteArrivals and EpubPage.remoteVersion announce. An image without both, and a font, size the layout, so a chapter laid out before they land keeps their absence for the life of this document, which keeps its pages and its page count. layoutOnly fetches just those. awaitLayoutResources waits for them within a time limit, for a caller that lays chapter out next. Without layoutOnly, it fetches every one the chapter names, an url() of a rule that matches no element included.

The fetches belong to the book, not to the caller: cancelling this call stops the wait, and the bytes still land for the next paint and the next document over the book.