More doc warnings
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=h1) Report
> Merging [#21808](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5cb5880d8f1647e303ba52487dc867db838fd6e0?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21808/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21808   +/-   ##
=======================================
  Coverage   91.95%   91.95%           
=======================================
  Files         160      160           
  Lines       49858    49858           
=======================================
  Hits        45845    45845           
  Misses       4013     4013
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.33% <100%> (ø)` | :arrow_up: |
| #single | `42.08% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/21808/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.63% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=footer). Last update [5cb5880...0446dba](https://codecov.io/gh/pandas-dev/pandas/pull/21808?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @TomAugspurger looks like still a couple of warnings, but reduced from before!