X00 Subfield $z - Geographic subdivision:

Subfield $z contains a geographic subject subdivision. Subfield $z is appropriate in the X00 fields only when a geographic subject subdivision is added to a name or name/title heading to form an extended subject heading .

Example:

100 0#$aFrederick$bII,$cHoly Roman Emperor,$d1194-1250$xHomes and haunts$zItaly