What was the intended function of the evaluate option for these ratings? I have searched the forums and web but found nothing.
Anything you would find useful in your workflow that could be powered by evaluating a variable or a code replacement that would map to a tag, color class, or rating.
The Tag item only works with numeric values: 0 or 1
The Rating item only works with numeric values: 0, 1, 2, 3, 4, and 5
The Color Class item works with numeric values ( 0 through 8 ) or the current set of Color Class labels as set in the General Preferences section of the Photo Mechanic Preferences dialog.
It is up to your imagination as to how to best use the feature, but here is an example. Let's say you shoot photos and video and you want to tag the videos only. If you set up a code replacement file like so:
video 1
still 0
audio 0
meta 0
unknown 0
and then you entered:
\{mediatype}\
into the Tag field of the IPTC Stationery Pad (after having set it to 'Evaluate') and applied it to your selected Contact Sheet items, the videos would be tagged and any tags on the rest of the items would be removed.
That's one example, but it is up to you decide how best to use the functionality in your workflow. We're providing you the tools to be creative in how you automate your workflow.
HTH,
-Kirk