The native C++ implementation of this method defines a default argument value. In the documentation generated for different libSBML language bindings, you may or may not see corresponding arguments in the method declarations. For example, in Java, a default argument is handled by declaring two separate methods, with one of them having the argument and the other one lacking the argument. However, the libSBML documentation will be identical for both methods. Consequently, if you are reading this and do not see an argument even though one is described, please look for descriptions of other variants of this method near where this one appears in the documentation.