[]

        # MatchData.[]

(from ruby core)
---
    mtch[i]               -> str or nil
    mtch[start, length]   -> array
    mtch[range]           -> array
    mtch[name]            -> str or nil

---

Match Reference -- MatchData acts as an array, and may be accessed using
the normal array indexing techniques.  `mtch[0]` is equivalent to the
special variable `$&`, and returns the entire matched string. 
`mtch[1]`, `mtch[2]`, and so on return the values of the matched
backreferences (portions of the pattern between parentheses).

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m          #=> #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
    m[0]       #=> "HX1138"
    m[1, 2]    #=> ["H", "X"]
    m[1..3]    #=> ["H", "X", "113"]
    m[-3, 2]   #=> ["X", "113"]

    m = /(?<foo>a+)b/.match("ccaaab")
    m          #=> #<MatchData "aaab" foo:"aaa">
    m["foo"]   #=> "aaa"
    m[:foo]    #=> "aaa"