Document the known undocumented functions/symbols

**Describe the bug**
The node-test `doc.test.js` has a list of symbols that are exported on a math instance, for which it is OK that they are not documented, because they are not intended for client use, for example. It has another, much longer, list of symbols that are exported on a math instance that really should have documentation , but don't. It uses this list to avoid the node tests always failing. But it doesn't make any fuss or warning, so there has been no impetus to complete the documentation and work toward the knownUndocumented getting down to the empty list, at which point it will become an error for there to be an undocumented exported symbol, and the knownUndocumented facility can be eliminated altogether.

This issue serves to keep track of the fact that there is missing documentation that needs to be added.