http://ruby-doc.org/core-1.8.7/MatchData.html

MatchData is the type of the special variable $~, and is the type of the object returned by Regexp#match and Regexp#last_match. It encapsulates all the results of a pattern match, results normally accessed through the special variables $&, $', $`, $1, $2, and so on. Matchdata is also known as MatchingData.

http://www.ruby-doc.org/core-2.0/MatchData.html

MatchData is the type of the special variable $~, and is the type of the object returned by Regexp#match and Regexp.last_match. It encapsulates all the results of a pattern match, results normally accessed through the special variables $&, $', $`, $1, $2, and so on.

2.0

mtch[i] → str or nil

1.8.7

mtch[i] => obj

这是啥意思呢？