Choose:
AddElement(object, true, false);
AddElement(object, true, true);
AddElement(object, false, false);
AddElement(object, false, true);
or AddElement(object, visible::on, deletable::off);
AddElement(object, visible::on, deletable::on);
AddElement(object, visible::off, deletable::off);
AddElement(object, visible::off, deletable::on);
The latter is more readable, you can spot bugs easier, you don't need to remember which parameter was for visibility, and which was for indicating deletable. And it doesn't take much more to write this than a confusing boolean. It doesn't scale.