Thanks Terry, I will start PEP8-checking my code before I submit (as well as testing more thoroughly). I was thinking the same thing about the logic behind _decode and index functions needing to be combined.

How would you recommend adding functionality to the decode function to handle expressions like "1.2 +5 chars" or "1.0 lineend-5c"? AutoComplete.py (#18409) uses this kind of index, so it will be needed soon. I'm thinking that splitting off the base index then parsing the remaining modifier expressions is the way to go.

I was also thinking that a _checkIndex method would be good to have especially when using the +/-line and +/-char expressions.