You can check in a metadata placeholder without specifying a primary file by entering an invalid path in the Primary File field. For example, entering the word placeholder into the Primary File field creates a content item within Content Server with the specified metadata, but no indexed primary file. Placeholders are useful for initiating workflows or making metadata available for searching and discussion.
If you are checking in a placeholder using Internet Explorer version 6.0 on the Windows XP operating system with Service Pack 2 installed, the path used in the Primary File field must be valid, but end with an invalid file. In the following example, c:/ is a valid drive, but placeholder is not a valid file:
If you do not specify a valid drive, an error message is displayed. Pretty clever way of forcing a meta-only content item without the configurations in place!
It's always worth reading the docs!