class Spec::Runner::CommandLine

def run(instance_rspec_options)

and +out+ are the streams output will be written to.
Runs specs. +argv+ is the commandline args as per the spec commandline API, +err+ 
def run(instance_rspec_options)
  # NOTE - this call to init_rspec_options is not spec'd, but neither is any of this
  # swapping of $rspec_options. That is all here to enable rspec to run against itself
  # and maintain coverage in a single process. Therefore, DO NOT mess with this stuff
  # unless you know what you are doing!
  init_rspec_options(instance_rspec_options)
  orig_rspec_options = rspec_options
  begin
    $rspec_options = instance_rspec_options
    return $rspec_options.run_examples
  ensure
    ::Spec.run = true
    $rspec_options = orig_rspec_options
  end
end