fail should be provided a map with error information as well as arguments bound.

[james-jw]

When a fail callback is called. It should be provided a single argument which is map that contains all the error information.

I propose:

map {
  'err': {
     'description': Same as standard error bindings
     ...
   },
  'args': array [ ... ]
}

This way, the fail callback has the information needed to either report a useful error, including the bad arguments or continue the work somehow.

[james-jw]

The work function should also be included, in case you want to do a retry.

map {
  'err': {
     'description': Same as standard error bindings
     ...
   },
  'args': array [ ... ]
  'deferred': function#
}

[ChristianGruen]

Related: W3 Bugzilla #29264, proposed by @apb2006.

[james-jw]

Fail is now provided a map as proposed by @apb2006!

The additional argument is populated with a map containing the deferred and the arguments. This will allow a callback to, for example retry if it gets a busy response.

Additionally error handing has been greatly improved. Errors are now properly reported in BaseX, as well as potential bugs. Also, the fail logic has been revised and properly documented in the ReadMe.

f06b682

c18ec61