Dir.glob mystery: Where are the FNM_xxx flags described? (SOLVED)

Dir.glob provides an optional parameter, usually referred as ‘flags’.
Where can I find a documentation about what flags are possible?

The Ruby docs just say that the flags are “the same as used in
File.fnmatch”.

Looking up the documentation of File.fnmatch, I only find the
explanation that these are the “FNM_xxx” flags, which can be or’ed
together. I could however find no documentation about what FNM_xxx flags
exist.

Where is this described?

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EDIT:

After not getting an answer here, I crossposted it and received the
following answer: