We should elaborate on how this `coords` object behaves.  The above line only works if the transformation object actually has this axis ordering, right?  (i.e. in FITS WCS, there is nothing in the definition that makes certain the axes appear in this order, and in the wild files are often reversed).  So this sort code should be avoided in examples and in practice (unless the code really can assume things about the input FITS file), instead:

```
ra = ax.coords['ra']
dec = ax.coords['dec']
```

Am I correct?  Mainly I just want to confirm my assumptions about this object.