anchor.diff:     : [ \t\r\n]+ -> skip
      ;
   
  +DIGIT
  +   : [0-9]
  +   ;
  +
  +ALPHA
  +   : [A-Za-z]
  +   ;
  +
  +IDENTIFIER
  +   : (ALPHA | '_') (ALPHA | DIGIT | '_')*
  +   ;
  +
  +TAG
  +   : ':' IDENTIFIER
  +   ;
   
      // a single octet other than NUL, CR, or LF
      
  
positive.code:    : stringlist
     | string
     | NUMBER
     | tag
     ;
  
  testlist
  
negative.code:    : '\\' OCTETNOTQSPECIAL
     ;
  
  comparator
     : ':comparator' string
     ;
  