question

The indexOf method was added in 17.2. There is no analogous command in 17.0, however you could use the groupmember command and a for loop to get the same functionality:

//indexOf

string group = "Group1";
treenode obj = model().find("Processor1");

for(int i = 1; i <= groupnummembers(group); i++) {
	if(groupmember(group, i) == obj )
		return i;
}
return -1;