Issue #14424: Document PyType_GenericAlloc, and fix the documentation of PyType_GenericNew

Doc/c-api/type.rst

@@ -70,13 +70,14 @@ Type Objects
 
 .. c:function:: PyObject* PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
 
-   XXX: Document.
-
+   Generic handler for the :attr:`tp_alloc` slot of a type object.  Use
+   Python's default memory allocation mechanism to allocate a new instance and
+   initialize all its contents to *NULL*.
 
 .. c:function:: PyObject* PyType_GenericNew(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
-   Generic handler for the :attr:`tp_new` slot of a type object.  Initialize
-   all instance variables to *NULL*.
+   Generic handler for the :attr:`tp_new` slot of a type object.  Create a
+   new instance using the type's :attr:`tp_alloc` slot.
 
 .. c:function:: int PyType_Ready(PyTypeObject *type)