Document internal functions with simple "///" doc comments
Document public properties/types/no-arg methods with simple "///" doc comments
Document public functions/methods with arguments with proper XML doc comments "///
..." including param/return docs
On each run make one or more PRs for this work, you don't have to do the whole job all at once. To avoid merge conflicts please check the files aren't currently being modified by any open PR
This issue should remain open until we're satisfied it's been complete, do not use "Fixes #NN" etc. in PR descriptions as we don't want this issue auto-closed