transform_image wcs update

Sorry if this is a silly question, but where in transform_image does the wcs get updated after the transformation is done? I don't see anything in the code that looks like it's doing this, but maybe that's somewhere else in the data class? This isn't really high priority or anything, I was just curious.

http://ccdproc.readthedocs.io/en/latest/_modules/ccdproc/core.html#transform_image

Thanks!