public static int extractFieldNumber(String nm) {
		int pos = nm.indexOf(BASENAME);
		if (pos < 0) {
			return -1;
		}
		int endpos = nm.indexOf('_', pos);
		if (endpos < 0) {
			return -1;
		}
		return Integer.decode(nm.substring(pos + BASENAME.length(), endpos)) - 1;
	}
The actual field number is encoded in the symbol name
@param nm is the symbol name
@return the field number or -1 if we cannot parse
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/UnionFacetSymbol.java