For a `get` operation, the helper should produce a list of attributes
on stdout in the same format. A helper is free to produce a subset, or
even no values at all if it has nothing useful to provide. Any provided
-attributes will overwrite those already known about by Git.
+attributes will overwrite those already known about by Git. If a helper
+outputs a `quit` attribute with a value of `true` or `1`, no further
+helpers will be consulted, nor will the user be prompted (if no
+credential has been provided, the operation will then fail).
For a `store` or `erase` operation, the helper's output is ignored.
If it fails to perform the requested operation, it may complain to