bpo-5945: Improve mappings and sequences C API docs. (GH-7029)

diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index 754dedc..f0b2005 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -379,8 +379,8 @@
    parameters must be non-*NULL*.
 
 
-.. c:function:: Py_ssize_t PyObject_Length(PyObject *o)
-               Py_ssize_t PyObject_Size(PyObject *o)
+.. c:function:: Py_ssize_t PyObject_Size(PyObject *o)
+               Py_ssize_t PyObject_Length(PyObject *o)
 
    .. index:: builtin: len
 
@@ -414,8 +414,8 @@
 
 .. c:function:: int PyObject_DelItem(PyObject *o, PyObject *key)
 
-   Delete the mapping for *key* from *o*.  Returns ``-1`` on failure. This is the
-   equivalent of the Python statement ``del o[key]``.
+   Remove the mapping for the object *key* from the object *o*.  Return ``-1``
+   on failure.  This is equivalent to the Python statement ``del o[key]``.
 
 
 .. c:function:: PyObject* PyObject_Dir(PyObject *o)