Block local variables:

  # {normal args; local variables}
  d = 2
  a = lambda{|;d| d = 1}
  a.call()
  d             # => 2

I think embedding language specific items in comments is silly since
you then have no mechanism to comment them out. Create a directive for
these extensions so that they behave as other parts of the language and
abide by the standard placement rules. Such as, things that are
commented out are not executed and thus ignored.