The C++ part of the API reference is incomplete. Missing information can be looked up in the older Doxygen reference:
panda3d - Core library
direct - Python support library
DIRECT is a set of Python-based tools that are layered on top of core Panda3D, which is written in C++. It includes the DirectGUI tools, the task system, the Interval system, a high-level class for animated characters, and several other systems.
There are additional C++ classes to support these modules, which can be found
Since this module is written in Python, it is not available to C++ programs. To switch to the Python version of the manual, use the link in the sidebar.