split a source file into multiple pages

[titaniumbones]

There is lots of documentation about how to assemble a book from many small files. Is it possible to work in the opposite direction, by keeping whole Parts in a single file? I'd like to keep my individual web pages relatively short and digestible, but I find that is a frustrating as an author. My preference would be to e.g. take each first-level header in a markdown page as a chapter or section.

This may be a bias that comes from org-mode, where it's fairly common to keep a mono-sourefile with many headings. Do you have any advice? thanks.