Step errors

We have established error codes for static and dynamic pipeline
errors, but what do we expect implementors to do with the errors that
come from a step.

Consider XInclude, there are at least three ways it can fail:

1. Malformed xi:include element
2. Resource error with no fallback
3. Circular inclusion

When the XInclude step fails, what error code should it raise? Do we
want to have a generic "step failed" error code? On the one hand, more
information would be nice, on the other, getting interoperable error
codes for all steps seems hopeless.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Whatever else we are intended to do, we
http://nwalsh.com/            | are not intended to succeed: failure is
                              | the fate allotted.--Robert Louis
                              | Stevenson