Hash with completion search feature. See OptionParser::Completion.

Methods
M
Included Modules
Instance Public methods
match(key)

Completion for hash key.

Source: show 

# File lib/optparse.rb, line 717
def match(key)
  *values = fetch(key) {
    raise AmbiguousArgument, catch(:ambiguous) {return complete(key)}
  }
  return key, *values
end