anchor.diff:      :   TAG_START_VERSION
           NAME_NUM ATTR_EQ ATTR_VALUE_START v=INT ATTR_VALUE_END
           TAG_CLOSE
  -        doc=SHORTDOC*
  +        (doc=SHORTDOC)*
           TAG_END_VERSION SHORTDOC*
   /*
   <version num="1.2.3">Game Name</version>
  
positive.code:         | anyattribute
          )*
          ( TAG_CLOSE
            doc=SHORTDOC*
            TAG_END_ADD
          | TAG_END
          )
  
negative.code:         | attr_expression_default
          | anyattribute
          )*
          ( TAG_CLOSE (doc+=SHORTDOC)* TAG_END_OPTION
          | TAG_END
          )
          SHORTDOC*
          -> ^(ENUMCONSTDEF ^(DOC $doc*) $name $value)
      ;
  
  structdefine
  