We moved some docs issues, because we no longer maintain them in forge. The things that that are to be documented in the documentation repos on Github were moved to issues in Github.
The original issue this issue is based on asked to document ext:filemetadata (which is a system extension and thus documented in core). I may have been wrong in moving it here, since it is probably better to be documented in Core API.
Sorry, I should have copied a little more context.
I am not really sure what should be documented for ext:filemetadata, if documentation is even necessary.
@Riccardo, I am closing this. If someone feels the need to document this, they must reopen or create new issue.
A new issue could be opened for TYPO3 Explained Issues, but I am not sure if this is really an area that is undocumented and should be documented, so if in doubt, just close here and do nothing.