(PHP 5, PHP 7, PHP 8)
    Each DOMDocument has a doctype
    attribute whose value is either null or a DOMDocumentType object.
   
$exclusive = false,$withComments = false,$xpath = null,$nsPrefixes = null$uri,$exclusive = false,$withComments = false,$xpath = null,$nsPrefixes = nullThe public identifier of the external subset.
The system identifier of the external subset. This may be an absolute URI or not.
       The name of DTD; i.e., the name immediately following the
       DOCTYPE keyword.
      
A DOMNamedNodeMap containing the general entities, both external and internal, declared in the DTD.
A DOMNamedNodeMap containing the notations declared in the DTD.
The internal subset as a string, or null if there is none. This does not contain the delimiting square brackets.