--- end(n)

    n ܤʬʸüΥեåȤ֤ޤ0 ϥޥå
    ̣ޤn ϰϳξ㳰 IndexError ȯ
    ޤn ܤʬʸ󤬥ޥåƤʤ nil 
    ֤ޤ

        /(foo)(bar)(BAZ)?/ =~ "foobarbaz"
        p $~.end(0)   # => 6
        p $~.end(1)   # => 3
        p $~.end(2)   # => 6
        p $~.end(3)   # => nil
        p $~.end(-1)  # => `end': index -1 out of matches (IndexError)

