add an option to escape the comma character in values field of a form field

it's impossible to have a comma in an option since the comma is used as a separator. Either use another, less common separator (like ;) or provide support for escaping the separation with \.

The issue names no file, test, or entry point. Start by locating the form-field values parsing and rendering code, then reproduce an option containing a comma. Done means users can enter and receive a comma within one option without breaking comma-separated values, with coverage for the chosen escaping or separator behavior.

Written by the indexing model from the issue text.