I think the biggest issue here is not how to explain it clearly in the docs, but that a lot of users will not confirm this in the docs based on the combination of:

1. c{1,5} is similar to slicing, also similar to python list definition, and python sets, all of which allow spaces for readability.

2. there is no error or warning

3. c{1,5} having one meaning and c{1, 5} having completely different meaning with no warning is deeply weird unless you think thoroughly through all of the implications.

I would prefer a warning to be added. This leads to the question, where do you draw the line after which a warning is no longer added?

I think I would allow this form as the most extreme where warning is still shown:

c{    1,     5      }

For any extra commas, newlines, etc, I would not show warnings because they look/feel different enough vs. {1,5}.

It seems to me that VERBOSE should have no effect inside of {1,5}.