How do you make custom fields made in document types mandatory?

Summary:

I can't make document types flexfields mandatory.

Content (required):

Hi,

I made the document type flexfield. Now I can't make the document type flexfields mandatory, is it possible to make them mandatory?

Thank you,

Selene

Version (include the version you are using, if applicable):

23B

Code Snippet (add any code snippets that support your topic, if applicable):