> Take a look at the indexing code in pandas

As the end-user, not quite my concern.

> and the staggering complexity of what's possible to put inside square brackets and how to decipher its meaning

I might not be aware of everything that's possible -- the usage I have of it doesn't give me an impression of staggering complexity. In fact I've found the functionality quite basic, and have been using pd.MultiIndex.from_* quite extensively for anything slightly more advanced than selecting a bunch of values at some level of the index.