anchor.diff:          ;
   
   postfixExpression
  -    :   atom
  +    :   atom //should be ID (and maybe allow STRING too)
       |   postfixExpression '[' expr ']'
       |   postfixExpression '(' argumentExpressionList? ')'
       |   postfixExpression '.' ID                            # attributeLookup 
  
positive.code: endIfStmt:  '{%' 'end' '%}' ;    
  
  /*
  // TODO should be in the expr rule!
  boolExpr:   expr op=('=='|'!='|'<'|'>'|'<='|'>=') expr    # exprComparison
          |   boolExpr op=('=='|'!=') boolExpr            # boolComparison
          |   boolExpr op=('and'|'or'|'&&'|'||') boolExpr    # boolExprCombination
  
negative.code: 
  /**
   * Output a variable (shortcut for {% print $var %})
   **/
  outputVariable: '{{' expr (END_OUTPUT|END_OUTPUT_WS) ;
  
  