Workflow condition based on Revision

We use a revision like . where major rev is a number and minor rev is a character starting with - , a, b and c.

On a major revision the user can make only 3 minor revisions. All the working well but I want to make a condition for a workflow (in properties) that only files with revision like %.- or %.a or %.b can enter in that workflow.

I try condition on Revision or on variable Revision like:

!=%.c

%.[-ab]

[0-30].[-ab]

and none works.

Even I forced a explicit condition like 0.c. It doesn't work. It is like no condition, on revision, exists.

We use PDMWE 2008 sp.5

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