Regular expression syntax for rep.get.prims

We were trying to write a script that can assign labels to objects that appear in within unpredictable prim hierarchies. For instance, we have ‘cracks’ that appear in several places in objects. (controlled procedurally outside of Omni)
To assign the right class label, we are a) naming all of the crack ‘object’ as crack_[number]. and b) use rep.get.prims(path_pattern. The documentation for path_patterns says to utilize “regular expressions” but haven’t had success. Any pointers?
Here is the code that does not work: (edited)

cracks=rep.get.prims(path_pattern=“/Replicator/Ref_Xform/Ref/crack”)
rep.modify.semantics(semantics=[(“class”, “crack”)], input_prims=cracks)

Are there any patterns, examples of what kinds of string matching and wilcards is supported?