diff --git a/src/wp-includes/html-api/class-wp-html-tag-processor.php b/src/wp-includes/html-api/class-wp-html-tag-processor.php
index ea74410230954..4cb3092f6c0a5 100644
--- a/src/wp-includes/html-api/class-wp-html-tag-processor.php
+++ b/src/wp-includes/html-api/class-wp-html-tag-processor.php
@@ -378,6 +378,31 @@ class WP_HTML_Tag_Processor {
 	 */
 	private $is_closing_tag;
 
+	/**
+	 * What kind of node was parsed in the last step while scanning through the document,
+	 * or if the parser hasn't paused on a matched token, then `null`.
+	 *
+	 * Can be one of:
+	 *   - WP_HTML_Tag_Processor::ELEMENT_NODE
+	 *   - WP_HTML_Tag_Processor::TEXT_NODE
+	 *   - WP_HTML_Tag_Processor::CDATA_SECTION_NODE
+	 *   - WP_HTML_Tag_Processor::PROCESSING_INSTRUCTION_NODE
+	 *   - WP_HTML_Tag_Processor::COMMENT_NODE
+	 *   - WP_HTML_Tag_Processor::DOCUMENT_TYPE_NODE
+	 *   - WP_HTML_Tag_Processor::WP_FUNKY_COMMENT_NODE
+	 *
+	 * @var string|null
+	 */
+	private $last_token_type = null;
+
+	/**
+	 * In what mode the parser should resume after pausing,
+	 * or if not paused on a matched token, then `null`.
+	 *
+	 * @var string|null
+	 */
+	private $continuation_state = null;
+
 	/**
 	 * Lazily-built index of attributes found within an HTML tag, keyed by the attribute name.
 	 *
@@ -567,7 +592,7 @@ public function next_tag( $query = null ) {
 				return false;
 			}
 			$this->tag_ends_at          = $tag_ends_at;
-			$this->bytes_already_parsed = $tag_ends_at;
+			$this->bytes_already_parsed = min( strlen( $this->html ) - 1, $tag_ends_at + 1 );
 
 			// Finally, check if the parsed tag and its attributes match the search query.
 			if ( $this->matches() ) {
@@ -2447,4 +2472,17 @@ private function matches() {
 
 		return true;
 	}
+
+	// Constants that would otherwise be noisy at the top of the file.
+
+	const ELEMENT_NODE                = 'NodeType.1.ELEMENT_NODE';
+	const TEXT_NODE                   = 'NodeType.3.TEXT_NODE';
+	const CDATA_SECTION_NODE          = 'NodeType.4.CDATA_SECTION_NODE';
+	const PROCESSING_INSTRUCTION_NODE = 'NodeType.7.PROCESSING_INSTRUCTION_NODE';
+	const COMMENT_NODE                = 'NodeType.8.COMMENT_NODE';
+	const DOCUMENT_TYPE_NODE          = 'NodeType.10.DOCUMENT_TYPE_NODE';
+	const WP_FUNKY_COMMENT_NODE       = 'NodeType.0_1.WP_FUNKY_COMMENT_NODE';
+
+	const STATE_COMPLETE = 'The parser has finished scanning through the document.';
+	const STATE_IN_TAG   = 'The parser has found a valid tag name and needs to continue parsing attributes.';
 }