question: public void putIdentifier ( String idName , Element element ) { if ( element == null ) { removeIdentifier ( idName ) ; return ; } if ( needsSyncData ( ) ) { synchronizeData ( ) ; } if ( identifiers == null ) { identifiers = new Hashtable ( ) ; } identifiers . put ( idName , element ) ; }
target:  Registers an identifier name with a specified element node. If the identifier is already registered, the new element node replaces the previous node. If the specified element node is null, removeIdentifier() is called.