pub fn read_documents_checked(
paths: &[String],
check: &dyn Fn(&Value, &str) -> Result<(), String>,
) -> Result<(Value, Vec<(String, Format)>), String>Expand description
read_documents with a caller-supplied per-file check (the v2 settings
typing, or none) — check(doc, "config file <path>") runs before the merge
so an unknown key is attributed to its file.