Relax assumptions on param names beyond alpha-numeric without `_`

We now have a safeguard that makes sure parameter names are Alphanumeric.
This may have been a bit to strict, we could e.g. at least include `.` as natural separators.
Originally raised by @krishnbera

Start by locating the safeguard that enforces alphanumeric parameter names and inspect how parameter names are validated. Confirm the intended separator behavior, including periods, while preserving existing support for underscores and alphanumeric names; done means the validation accepts the agreed names without weakening unrelated checks.

Written by the indexing model from the issue text.