Correct unknown DOCTYPE checking

lib/ParseError.php

@@ -60,16 +60,18 @@ class ParseError {
     const EXPECTED_DOCTYPE_BUT_GOT_END_TAG                                  = 201;
     const EXPECTED_DOCTYPE_BUT_GOT_CHARS                                    = 202;
     const EXPECTED_DOCTYPE_BUT_GOT_EOF                                      = 203;
-    const UNEXPECTED_DOCTYPE                                                = 204;
-    const UNEXPECTED_START_TAG                                              = 205;
-    const UNEXPECTED_END_TAG                                                = 206; // html5lib also uses 'adoption-agency-1.2' and 'adoption-agency-1.3' for this
-    const NON_VOID_HTML_ELEMENT_START_TAG_WITH_TRAILING_SOLIDUS             = 207;
+    const UNKNOWN_DOCTYPE                                                   = 204;
+    const UNEXPECTED_DOCTYPE                                                = 205;
+    const UNEXPECTED_START_TAG                                              = 206;
+    const UNEXPECTED_END_TAG                                                = 207; // html5lib also uses 'adoption-agency-1.2' and 'adoption-agency-1.3' for this
+    const NON_VOID_HTML_ELEMENT_START_TAG_WITH_TRAILING_SOLIDUS             = 208;
 
     const MESSAGES = [
         self::EXPECTED_DOCTYPE_BUT_GOT_START_TAG                                => 'Expected DOCTYPE but got start tag',
         self::EXPECTED_DOCTYPE_BUT_GOT_END_TAG                                  => 'Expected DOCTYPE but got end tag',
         self::EXPECTED_DOCTYPE_BUT_GOT_CHARS                                    => 'Expected DOCTYPE but got characters',
         self::EXPECTED_DOCTYPE_BUT_GOT_EOF                                      => 'Expected DOCTYPE but got end-of-file',
+        self::UNKNOWN_DOCTYPE                                                   => 'Unknown DOCTYPE',
         self::UNEXPECTED_START_TAG                                              => 'Unexpected start tag',
         self::UNEXPECTED_END_TAG                                                => 'Unexpected end tag',
         self::NON_VOID_HTML_ELEMENT_START_TAG_WITH_TRAILING_SOLIDUS             => 'Trailing solidus in non-void HTML element start tag',

lib/Token.php

@@ -27,7 +27,7 @@ class DOCTYPEToken extends Token {
     public $public;
     public $system;
 
-    public function __construct(string $name = null, string $public = null, string $system = null) {
+    public function __construct(?string $name = null, ?string $public = null, ?string $system = null) {
         // null stands in for the distinct "missing" state
         $this->name = $name;
         $this->public = $public;

lib/TreeBuilder.php

@@ -240,8 +240,8 @@ class TreeBuilder {
                 # If the DOCTYPE token's name is not "html", or the token's public identifier is
                 #   not missing, or the token's system identifier is neither missing nor 
                 #   "about:legacy-compat", then there is a parse error.
-                if ($token->name !== 'html' || $token->public !== '' || ($token->system !== '' && $token->system !== 'about:legacy-compat')) {
-                    $this->error(ParseError::INVALID_DOCTYPE);
+                if ($token->name !== 'html' || $token->public !== null || !($token->system === null || $token->system === 'about:legacy-compat')) {
+                    $this->error(ParseError::UNKNOWN_DOCTYPE);
                 }
 
                 # Append a DocumentType node to the Document node, with the name attribute set
@@ -1926,7 +1926,7 @@ class TreeBuilder {
         }
     }
 
-    public static function insertCommentToken(CommentToken $token, \DOMNode $position = null) {
+    public function insertCommentToken(CommentToken $token, \DOMNode $position = null) {
         # When the steps below require the user agent to insert a comment while
         # processing a comment token, optionally with an explicitly insertion position
         # position, the user agent must run the following steps: