Where is the help function defined?

[Peng Yu]

help(help) gives me the following explanation.

##################
Help on _Helper in module site object:

class _Helper(__builtin__.object)
 |  Define the built-in 'help'.
 |  This is a wrapper around pydoc.help (with a twist).
 |
 |  Methods defined here:
 |
 |  __call__(self, *args, **kwds)
 |
 |  __repr__(self)
 |
 |
----------------------------------------------------------------------
 |  Data descriptors defined here:
 |
 |  __dict__
 |      dictionary for instance variables (if defined)
 |
 |  __weakref__
 |      list of weak references to the object (if defined)
###################

I then looked at pydoc site. But I don't see an entry on help(). How
to figure out where help() (or a function in general) is defined?