Categorie and Supplemental Categories

These fields have been deprecated for 25 years, you may want to switch to using something else.

Categories is limited to 3 7-bit ASCII characters and SupplimentalCategories is an unordered array so you can read and write these with a script or EXIFTool.

try{
	thumbs = app.document.selections;
	//get file metadata
	var descMeta = thumbs[0].synchronousMetadata;
	var descXMP = new XMPMeta(descMeta.serialize());
	//define vars
	var newDescr = '';
	var descr = 'A';
	var descr2 = 'B';
	//remove old values
	descXMP.deleteProperty('http://ns.adobe.com/photoshop/1.0/', 'SupplementalCategories');
	descXMP.deleteProperty('http://ns.adobe.com/photoshop/1.0/', 'Category');
	//set new values
	descXMP.appendArrayItem('http://ns.adobe.com/photoshop/1.0/', 'SupplementalCategories', descr2, 0, XMPConst.PROP_IS_ARRAY);
	descXMP.setProperty('http://ns.adobe.com/photoshop/1.0/', 'Category', descr);
	//update file
	var descUpdatedPacket = descXMP.serialize(XMPConst.SERIALIZE_OMIT_PACKET_WRAPPER | XMPConst.SERIALIZE_USE_COMPACT_FORMAT);
	thumbs[0].metadata = new Metadata(descUpdatedPacket);
	//read new metadata from file
	descMeta = thumbs[0].synchronousMetadata;
	newDescr = descMeta.read('http://ns.adobe.com/photoshop/1.0/', 'Category').toString();
	newDescr = newDescr + ' ' + descMeta.read('http://ns.adobe.com/photoshop/1.0/', 'SupplementalCategories').toString();
	Window.alert(newDescr);
	}
catch(e){
	}