module CodeRay::PluginHost

def validate_id id

given String includes non-alphanumeric characters (\W).
Raises +ArgumentError+ for all other objects, or if the

or returns +id+ if it already is a Symbol.
Converts +id+ to a Symbol if it is a String, 
def validate_id id
  if id.is_a? Symbol or id.nil?
    id
  elsif id.is_a? String
    if id[/\w+/] == id
      id.downcase.to_sym
    else
      raise ArgumentError, "Invalid id given: #{id}"
    end
  else
    raise ArgumentError, "String or Symbol expected, but #{id.class} given."
  end
end