The markdown_fold tool is built from sources/markdown_fold. Its purpose is to ensure that the verbatim portions of markdown files are not overlong for the purposes of printing in a 6x9 inch book.
This tool uses markdown_fold as part of the book building script to keep all the markdown and example files within the gutter limits; the errors we used to get were text going too far into the right hand side margin.
The manuscript indexes all items referencing a trademark upon their first instance. We have this tool to pick up such references and make a complete list of trademark references, so that later on in the text, we do not need to announce the word as trademarked.
This tool works out if there is a localised version of the given file and emits that as the path, otherwise it emits the en (English) version of the file. This means that the localised copy should have a safe fallback whenever new files are added which have not yet been localised.