[2.3] Fixes various phpdoc and coding standards.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

This is not an `@var` doc but `@see`. Shall we also use a `use` statement for them?