fix typos.
minor #3988 fix typos. (yositani2002)

This PR was merged into the 2.3 branch.

Discussion
----------

fix typos.

two notes and one caution dose not show.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Commits
-------

5402121 fix typos.