Should isEditable() be iterative instead of recursive?

[ProfJanetDavis]

Since isEditable() is tail recursive, it could be re-written using a while loop instead of recursion. That would probably be a bit less elegant, but might be a bit more efficient. It would also be a bit of work to do.

Evaluate this from a performance perspective:

• Is an appreciable part of the total runtime spent in the isEditable() function?
• If so, is the iterative algorithm appreciably faster than the current, recursive algorithm?

Note the same will apply to the isVisible() function proposed as part of the solution to #49. If isVisible() exists, the same considerations will apply. If both questions about isEditable() above are answered "no", ask the same questions for isVisible().