code: func (p *pageState) sourceRef() string {
  	if !p.File().IsZero() {
  		sourcePath := p.File().Path()
  		if sourcePath != "" {
  			return "/" + filepath.ToSlash(sourcePath)
  		}
  	}
  
  	if len(p.SectionsEntries()) > 0 {
  		// no backing file, return the virtual source path
  		return "/" + p.SectionsPath()
  	}
  
  	return ""
  }
docs: // sourceRef returns the reference used by GetPage and ref/relref shortcodes to refer to
  // this page. It is prefixed with a "/".
  //
  // For pages that have a source file, it is returns the path to this file as an
  // absolute path rooted in this site's content dir.
  // For pages that do not (sections witout content page etc.), it returns the
  // virtual path, consistent with where you would add a source file.