paval求解

对parval()，属性指向很困扰
比如： baynumber = parval(2)，求注解下，为什么是（2），

如果levelnuber=?????  求注解。。。。
For developer use. This command is used inside a function that is called by the nodefunction() command. It returns the parameter passed to nodefunction specified by index as a number. The first additional parameter passed to nodefunction() is parameter 1, the second is parameter 2, etc. Parameters can also be retrieved using parnode() and parstr() for casting them as a treenode and string respectively.
Example: double passedval = parval(3);

This sets passedval equal to the number that was passed to nodefunction() as parameter 3.