DOC: Reindexing behaviour of dataframe column-assignment missing
- [X] xref #39845 (.loc[] portion of issue)
- [X] tests added / passed
- [X] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

Do we need a whatsnew entry for a documentation-only issue? If so, where and in what general format to we put it? Don't think we need a whatsnew, you can not use closes if you are fixing part of the issue, because this would close the issue. E.g. your number is wrong, you are referencing the pr This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. > This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this.

I apologize for the lack of activity. I was very busy with finals and will be working towards closing this pull request in the coming days. Hello @hewittk! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-06-09 21:14:12 UTC This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Sorry this went un-reviewed for a while. Could you merge master again to this branch? Thanks for the PR, but it appears to have gone stale. Let us know if you're still interested in working on this and we can reopen. Closing.