We would want to validate the regular expression options according to the BSON spec:

Options are identified by characters, which must be stored in alphabetical order. Valid options are 'i' for case insensitive matching, 'm' for multiline matching, 'x' for verbose mode, 'l' to make \w, \W, etc. locale dependent, 's' for dotall mode ('.' matches everything), and 'u' to make \w, \W, etc. match unicode.????

We would want return warnings when running the validate command with/without the checkBSONConsistency: true option.

There might not be an existing interface in our jstest to insert non-conformant regex documents, so we would want to use wt tool to manually inject them. See example.