code: func (ec ErrClass) EqualClass(err error) bool {
  	e := errors.Cause(err)
  	if e == nil {
  		return false
  	}
  	if te, ok := e.(*Error); ok {
  		return te.class == ec
  	}
  	return false
  }
docs: // EqualClass returns true if err is *Error with the same class.