Private/undocumented history object properties

I wanted a way to do Buffer.history_forward() and Buffer.history_backward(), but skipping over the duplicates. I was able to implement that, but I needed to use private and/or undocumented properties, which I'd prefer not to do. I'm guessing a lot of this is just a matter of what docstrings happen to be filled in at this point, and there wasn't any specific intent with these items regarding what should/shouldn't be in the "official" API. If that's the case, I'd be happy provide pull requests to help fill some of these in. But just to confirm...

• The (documented) Buffer.go_to_history() method takes an argument for the item position, but I don't see any obvious documented way to get the max value allowed (like using the history list itself). In other words, how would a user of the API know the range of valid values that can be passed in? For now, I'm using the length of the undocumented _working_lines attribute, which is what other code within the library does.
• What is the best way to get a copy of the history itself (without unnecessary side effects -- e.g. by calling History.load_history_strings), other than using an undocumented attribute like _working_lines (or something complicated involving subclassing History)?
• I see that I can get the current position in history from the working_index attribute. It seems to be semi-documented -- It's mentioned in passing twice in the documentation, but isn't explicitly documented as a property with a description. Is it safe to use that, as far as API stability?

I can put together pull requests to address some or all of the above, if those would be welcome. Specifically:

• Adding an official property to Buffer for "working_lines" (or "history_lines", or something) that either returns self._working_lines or something like list(self._working_lines).
• Maybe add a "history_count" or "history_length" that returns len(self._working_lines), unless that's overkill (if the above is added anyway).
• Documenting the working_index property. (Just needs a docstring?)
• If others are interested in something like a "skip_dups" flag for the history_forward() and history_backward() methods, I could include code for that as well, with doc updates.

Review Buffer.go_to_history(), history_forward(), history_backward(), the History class, _working_lines, and working_index to understand the current history API. Define the intended public properties or duplicate-skipping behavior, then document and validate the agreed interface and its valid history range.