code: func (a *Annotator) InternalReason(reason string, args ...interface{}) *Annotator {
  	if a == nil {
  		return a
  	}
  	a.ctx.internalReason = fmt.Sprintf(reason, args...)
  	return a
  }
docs: // InternalReason adds a stack-trace-only internal reason string (for humans) to
  // this error.
  //
  // The text here will only be visible when using `errors.Log` or
  // `errors.RenderStack`, not when calling the .Error() method of the resulting
  // error.
  //
  // The `reason` string is formatted with `args` and may contain Sprintf-style
  // formatting directives.