anchor.diff:  
   <prop_list> ::= '(' <key_value_pair> ( ',' <key_value_pair> )* ')'
   
  -<key_value_pair> ::= <quoted_string> ':' ( <value> | <non_variable_value_list> )
  +<key_value_pair> ::= <quoted_string> ':' 
  +                     ( <value> | <python_style_list> | <python_style_dict> )
   
   <given_clause> ::= GIVEN FACET PARAM <facet_param_list>
   
  
positive.code: 
  <formal_parameter_decls> ::= <formal_parameter_decl> ( ',' <formal_parameter_decl> )*
  
  <formal_parameter_decl> := ...
  
  <model_block> ::= ( <block_statement> )+
  
  <block_statement> ::= ...
  
  <quoted_string> ::= '"' ( <char> )* '"'
                    | "'" ( <char> )* "'"
  
negative.code: <route_by_clause> ::= ROUTE BY <quoted_string>
  
  <relevance_model_clause> ::= USING RELEVANCE MODEL <identifier> <prop_list>
                               [<relevance_model>]
  
  <relevance_model> ::= DEFINED AS <formal_parameters> BEGIN <model_block> END
  
  