cassandra-stress tool: [a-z] letters range for varchar column

Question

Under cassandra-stress yaml config file, columnspec defines insert range of data.

For a varchar column how to say I want a column to be populated with words built from letters [a-z]* only?

If I say:

columnspec:
  - name: id # varchar
  - population: uniform(100..110)

I get stings like this: \x1c\x0b\x1bK]