Document rationale behind types of transitions

[ExpHP]

So, to my understanding, transitions are classified into:

• '', an epsilon transition
• 'a' or any other single character is a literal
• '.*' represents a glob * or a wildcard ?
• '**' is a globstar ** not covered by the following cases
• '**/' represents a **/ (except at the end)
• '**/*' represents the string **/*

The last two feel pretty ad-hoc. Do you recall why these special cases exist, and if so, could this be documented in the code? My best guesses so far are:

• I think **/ is necessary because **/a should be able to match "a", but if we represented it as ['**', 'a'] then toGlob would produce the ugly "**a".
• I think **/* only exists for better capture semantics, as otherwise the "**/" could greedily match characters after the final slash that ought to belong to the *.