anchor.diff:  
   maybe_cmd options{ backtrack=true; } :
        expr (t_FILLER? t_ASSIGN t_FILLER? expr)? t_FILLER?
  -  |  t_IDENTIFIER cmd_args //TODO-AC: re-enable once I figure out side-effects/backtracking
  +  //|  t_IDENTIFIER cmd_args //TODO-AC: re-enable once I figure out side-effects/backtracking
     ;
   
   cmd_args :
  
positive.code: 
  t_ASSIGN : ASSIGN { offsetTracker.advanceInLine(1); };
  
  t_LPAREN : LPAREN { offsetTracker.advanceInLine(1); };
  t_RPAREN : RPAREN { offsetTracker.advanceInLine(1); };
  t_LCURLY : LCURLY { offsetTracker.advanceInLine(1); };
  t_RCURLY : RCURLY { offsetTracker.advanceInLine(1); };
  t_LSQUARE : LSQUARE { offsetTracker.advanceInLine(1); };
  t_RSQUARE : RSQUARE { offsetTracker.advanceInLine(1); };
  
  t_IDENTIFIER : IDENTIFIER { offsetTracker.advanceByTextSize($text); };
  t_NUMBER : NUMBER { offsetTracker.advanceByTextSize($text); };
  
negative.code:   |  t_AT t_FILLER? name
    ;
  
  //TODO-AC: This is separate from expr because it allows t_COLON and t_END
  //  This shouldn't be necessary - dynamic scopes should handle this.
  //  See revision 709 for an implementation with dynamic scopes.
  