It would be cool to be able to refer to a field value interpolated within static text:
'genv.sites.code.with' = '#{regexify ''[a-c][1-3]''}',
'genv.sites.url.matching' = 'http://#(sites.valuecode).com'
This is already possible with Faker expressions:
'genv.topic.something.with' = 'xyz#{regexify ''[a-c][1-3]''}123'
In the top example, I used #() to differentiate from Faker interpolations. An idea of how it could be done, but not saying that it is the best way.
If there were a special syntax for splicing in values from other fields, it might not be necessary to have matching. The with could be something like:
'genv.topic.field.with' = 'ABC.#{regexify ''[a-c][1-3]''}.#(topic.value.other_field).XYZ',