This package is worthless in Go 1.13. It was also worthless to begin with seeing as the popular pkg/errors has the same functionality.
errctx is a simple Go library for adding context (in the form of strings) to errors in situations when an error occurs and is propagated back through a long call chain; each function in the call chain may or may not want to add context as to where/why/how the error occurred.
errctx produces error strings of the following form:
<third piece of context>: <second piece of context>: <first piece of context>: <root error message>
Yes, it is essentially a glorified way of writing
err = fmt.Errorf("%s: %s", "context", err.Error())
only one has the option to get the root error (and thus check its type) via errctx.Root(err).
See the in-source documentation for details. There is also a contrived example to take a look at.