TermIt

This issue concerns the new file dialog shown when attaching files to a document (new and existing).

1. React shows warnings that there is a missing onChange handler on the identifier field in the new file form. If the field is supposed to be read-only, it should be marked as such.
2. The value of the field does not change when the file name changes. This would indicate that the file identifier is not generated. Perhaps it is generated on persist, in which case there is no point in the field being there at all.
3. In case of the field being intentionally read-only the help text is misleading, because it indicates that the user should be able to edit the identifier (which is true in all other create-asset forms).

Tested on dev.