Since r46126 [Feature #9864], where OptParse was added as an alias for OptionParser, the complete class documentation for OptionParser leaks into the class documentation for Object.
lib/optparse.rb: [DOC] nodoc OptParse, introduced with r46126,
to avoid leaking of its documentation (OptionParser's docs) into
the class documentation of Object. [ruby-core:79909] [Bug #13281]