anchor.diff:      :   { tagMode && !attrMode }?=> 'cond'
       ;
   
  +NAME_VERCOND
  +    :   { tagMode && !attrMode }?=> 'vercond'
  +    ;
  +
   NAME_DEFAULT
       :   { tagMode && !attrMode }?=> 'default'
       ;
  
positive.code:         | TAG_END
          )
          SHORTDOC*
          // has_cond
          -> {has_ver1 && has_ver2 && has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  ^(OP_LOGICAL_AND[$TAG_START_ADD, "and"]
                      ^(OP_LOGICAL_AND[$TAG_START_ADD, "and"]
                          $ver1 $ver2)
                      $cond)
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          -> {has_ver1 && !has_ver2 && has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  ^(OP_LOGICAL_AND[$TAG_START_ADD, "and"] $ver1 $cond)
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          -> {!has_ver1 && has_ver2 && has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  ^(OP_LOGICAL_AND[$TAG_START_ADD, "and"] $ver2 $cond)
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          -> {!has_ver1 && !has_ver2 && has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  $cond
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          // !has_cond
          -> {has_ver1 && has_ver2 && !has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  ^(OP_LOGICAL_AND[$TAG_START_ADD, "and"] $ver1 $ver2)
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          -> {has_ver1 && !has_ver2 && !has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  $ver1
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
          -> {!has_ver1 && has_ver2 && !has_cond}?
             ^(IF[$TAG_START_ADD, "if"]
                  $ver2
                  ^(FIELDDEF ^(DOC $doc?) $type $name))
  
negative.code: 
  attr_expression_cond
      :   NAME_COND! ATTR_EQ! ATTR_VALUE_START! expression ATTR_VALUE_END!
      ;
  
  attr_expression_vercond
      :   NAME_VERCOND! ATTR_EQ! ATTR_VALUE_START! expression ATTR_VALUE_END!
      ;
  
  attr_expression_default
  