Tal, welcome back to Python and IDLE development.  3.5 only gets security fixes. 

Please post here a draft doc paragraph.  Before reading the code in detail, I will pull it into my repository and try to test it as a 'naive user' who has only read that paragraph.

'Large text' has two meanings: long lines and lots of lines.  The former bog down and eventually freeze tkinter Texts.  (tk 8.7.0, now in alpha, will feature a re-written Text widget that should solve this.)  Lots of (short) lines, at least up to a million, is not a problem for Text, but is for users scrolling back.  Which problem does squeezer attack?  Both?

As the comment at the top of tooltips.py says, it is currently unused. It is also untested.   Calltips uses a version of the code. Hence, I was planning to sometime delete tooptips.py.  If it to be kept, I would like to see if it can be revised (at least TooltipBase) so it can be used both by calltips_w.py and any new code, such as squeezer.  It needs docstrings and a complete test.  This would be a separate issue that is a dependency of this one.  Since the file is so short, TooltipBase might eventually be put in another file with something else.