Documented option "--deepen" is unknown to git-pull

Option "--deepen" is documented in online doc of git-pull, Sec.
_Options related to fetching_, see
    https://git-scm.com/docs/git-pull#Documentation/git-pull.txt---deepenltdepthgt
But executing "git pull --deepen=100 origin master" returns
    error: unknown option `deepen'

More tests show option "--deepen" is known to git-fetch but not
git-pull, although the doc of git-pull says
    git pull runs git fetch with the given parameters and calls git
    merge to merge the retrieved branch heads into the current branch.
    https://git-scm.com/docs/git-pull#_description
which suggests that every valid option of "git fetch" would also valid
for "git pull".

Is this a documentation or an implementation problem? (I use git v2.25.1.)

muzimuzhi