Misleading documentation for git-diff-files (diff-filter)

I originally asked this question on stackoverflow (https://stackoverflow.com/q/48039277).

I wanted to know if git diff-files shows files that are not in the index but are in the working tree. The documentation says you can supply --diff-filter=A, which will select file "that are added". However, git-diff-files (appears) to never show any files with the status of "A".

It seems like the cause is that git diff-files includes diff-options.txt which uses a standard template for --diff-filter which includes the "A" option. Perhaps a clarification can be added?

Compares the files in the working tree and the index. When paths are specified, compares only those named paths. Otherwise all entries in the index are compared. The output format is the same as for 'git diff-index' and 'git diff-tree'. Files not in the index are not compared.