It is described in the overall Angle doc string.
```
Wrapping
--------

Depending on the context, theta = 2pi radians and theta = 0 radians are the same thing.
If you want your angles to be wrapped to [-pi,pi) radians, you can do this by calling

    >>> theta = theta.wrap()

This could be appropriate before testing for the equality of two angles for example, or
calculating the difference between them.
```
(It was there before too, but this branch changes the syntax.)

I guess it would be a good idea to add similar text to `wrap` itself.  It's a C++ function, but we can insert the docstring in like we do in other places.