Quoting documentation:

"""
Package xcontext provides addons to std package context.

Merging contexts

Merge could be handy in situations where spawned job needs to be canceled
whenever any of 2 contexts becomes done. This frequently arises with service
methods that accept context as argument, and the service itself, on another
control line, could be instructed to become non-operational. For example:

	func (srv *Service) DoSomething(ctx context.Context) (err error) {
		defer xerr.Contextf(&err, "%s: do something", srv)

       		// srv.serveCtx is context that becomes canceled when srv is
       		// instructed to stop providing service.
       		origCtx := ctx
       		ctx, cancel := xcontext.Merge(ctx, srv.serveCtx)
       		defer cancel()

       		err = srv.doJob(ctx)
       		if err != nil {
       			if ctx.Err() != nil && origCtx.Err() == nil {
       				// error due to service shutdown
       				err = ErrServiceDown
       			}
       			return err
       		}

		...
	}
"""