How can I access a property's docstring and not that of the value it holds?

Why do the 2 help functions in the code below return different docstrings for `abc.x`?

```
class C(object):
    def __init__(self):
        self._x = None

    def getx(self):
        print "** In get **"
        return self._x

    x = property(getx, doc="I'm the 'x' property.")

abc = C()
help(abc) # prints the docstring specified for property 'x'
help(abc.x) # prints the docstring for "None", the value of the property

```