Remaining tasks for full publication of the "is" functions

- [ ] Declare Range and ResultSet types in `types/index.d.ts` and make the associated "is" functions into guards; also add type tests for them into `types/index.ts`
- [ ] Provide website documentation for the "is" functions for which it is missing.
- [ ] Make all of the exported "is" functions available in the Parser
- [ ] Make sure embedded docs are available for all "is" functions.