(PHP 5, PHP 7, PECL tidy >= 0.5.2)
tidy::isXml -- tidy_is_xml — Indicates if the document is a generic (non HTML/XHTML) XML document
面向对象风格
过程化风格
Tells if the document is a generic (non HTML/XHTML) XML document.
   This function returns TRUE if the specified tidy
   object is a generic XML document (non HTML/XHTML),
   or FALSE otherwise.
  
    This function is not yet implemented in the Tidylib itself, so it always
    return FALSE.