plug rules for static methods
minor #3864 plug rules for static methods (cordoval)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #3864).

Discussion
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plug rules for static methods

| Q             | A                   |
| ---           | ---                 |
| Doc fix?      | yes                  |
| New docs?     | no                 |
| Applies to    | 2.3+                |
| Fixed tickets | #3855               |
| License       | CC-ASA 3.0 Unported |

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Commits
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b7e4729 plug rules for static methods
2803-document-descriptors-and-descriptorhelper