class Rouge::TemplateLexer

HTML.
own default for the parent lexer, which is otherwise defaulted to
which language is being templated. The lexer class can specify its
A TemplateLexer is one that accepts a :parent option, to specify
@abstract

def parent

the parent lexer - the one being templated. 
def parent
  return @parent if instance_variable_defined? :@parent
  @parent = lexer_option(:parent) || Lexers::HTML.new(@options)
end