In message "[ruby-talk:02519] Re: frozen behavior"
    on 00/04/20, Yukihiro Matsumoto <matz / netlab.co.jp> writes:

||  Trying to modify String "Struct": can't modify frozen object
||  Trying to modify String "File": can't modify frozen object
||  Trying to modify String "Errno": can't modify frozen object
|
|I have no idea why they are frozen.  I'll check on them.

Checked.
They are internal shared string created by rb_str_dup().

							matz.