Review error message and docstrings

[Sparks29032]

Let's review the morph_error() function docstring and check all error messages to ensure they are returning what we want. There are 28 in total.

[sbillinge]

If possible, can we reuse this by way of documentation somehow? Either developer or user docs? Send like a lot of work for not that much gain otherwise (though would be useful once it is done)