Document discovery

The documents are the *.md files git ls-files --cached --others --exclude-standard lists from the root: tracked, or new and not yet added, but never ignored. A listed file that is gone from disk, a deletion not yet committed, is left out. Outside a Git repository, or without Git, every *.md under the root is a document.

Either way, a file under a directory of build output or dependencies is skipped, at any depth. Git usually ignores those already; skipping them covers a repository that does not. A file matching documents.exclude is no document either: Documents. Anything a repository wants checked but not formatted, or the other way round, is an exclusion in the configuration.

The root is the nearest directory, from the current one up, that holds a configuration file or .git, unless --root names it. Every document under it is read on every run, so links and anchors between documents resolve; the paths a command is given, or the current directory, only choose which of them are reported and rewritten.

Documents are read and written through a directory opened at the root with cap-std, so a fix never writes outside it, even through a symbolic link. A document must be UTF-8; one that is not stops the run with an error naming it.

The same set is what index expects the index document to link, so a document in a skipped directory never needs listing.