@Override
	public void decode(Decoder decoder, SleighLanguage sleigh) throws DecoderException {
//		int el = decoder.openElement(ELEM_USEROP);
		index = (int) decoder.readSignedInteger(ATTRIB_INDEX);
		decoder.closeElement(ELEM_USEROP.id());
	}
A user-defined pcode operation (PcodeOp)
This is implemented as a name and a unique id which is passed
as the first parameter to a PcodeOp with the opcode = "CALLOTHER".
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/processors/sleigh/symbol/UseropSymbol.java