code: func (ns *Namespace) RelLangURL(a interface{}) (template.HTML, error) {
  	s, err := cast.ToStringE(a)
  	if err != nil {
  		return "", err
  	}
  
  	return template.HTML(ns.deps.PathSpec.RelURL(s, !ns.multihost)), nil
  }
docs: // RelLangURL takes a given string and prepends the relative path according to a
  // page's position in the project directory structure and the current language.