
    
directive ::= 
               "\#" "doctest:" directive_options
    
directive_options ::= 
               directive_option ("," directive_option)*
    
directive_option ::= 
               on_or_off directive_option_name
    
on_or_off ::= 
               "+" | "-"
    
directive_option_name ::= 
               "DONT_ACCEPT_BLANKLINE" | "NORMALIZE_WHITESPACE" | ...
