diff --git a/lib/experimental/html/class-wp-html-tag-processor.php b/lib/experimental/html/class-wp-html-tag-processor.php
index 5dc5981ef15f78..49a81371fc006c 100644
--- a/lib/experimental/html/class-wp-html-tag-processor.php
+++ b/lib/experimental/html/class-wp-html-tag-processor.php
@@ -180,6 +180,7 @@
  * @since 6.2.0
  */
 class WP_HTML_Tag_Processor {
+	const MAX_BOOKMARKS = 10;
 
 	/**
 	 * The HTML document to parse.
@@ -362,6 +363,15 @@ class WP_HTML_Tag_Processor {
 	 */
 	private $classname_updates = array();
 
+	/**
+	 * Tracks a semantic location in the original HTML that shuffles
+	 * with the updates applied to the document.
+	 *
+	 * @since 6.2.0
+	 * @var array
+	 */
+	private $bookmarks = array();
+
 	const ADD_CLASS    = true;
 	const REMOVE_CLASS = false;
 	const SKIP_CLASS   = null;
@@ -479,6 +489,47 @@ public function next_tag( $query = null ) {
 		return true;
 	}
 
+
+	/**
+	 * Sets a bookmark in the HTML document.
+	 *
+	 * @param string $name Identifies this particular bookmark.
+	 * @return false|void
+	 */
+	public function set_bookmark( $name ) {
+		if ( null === $this->tag_name_starts_at ) {
+			return false;
+		}
+
+		if ( ! array_key_exists( $name, $this->bookmarks ) && count( $this->bookmarks ) > self::MAX_BOOKMARKS ) {
+			return false;
+		}
+
+		$this->bookmarks[ $name ] = new WP_HTML_Text_Replacement(
+			$this->tag_name_starts_at - 1,
+			$this->tag_ends_at,
+			''
+		);
+	}
+
+
+	/**
+	 * Removes a bookmark once it's not necessary anymore.
+	 *
+	 * @param string $name Name of the bookmark to remove.
+	 * @return bool
+	 */
+	public function release_bookmark( $name ) {
+
+		if ( ! array_key_exists( $name, $this->bookmarks ) ) {
+			return false;
+		}
+
+		unset( $this->bookmarks[ $name ] );
+		return true;
+	}
+
+
 	/**
 	 * Skips the contents of the title and textarea tags until an appropriate
 	 * tag closer is found.
@@ -1102,11 +1153,115 @@ private function apply_attributes_updates() {
 			$this->updated_html .= substr( $this->html, $this->updated_bytes, $diff->start - $this->updated_bytes );
 			$this->updated_html .= $diff->text;
 			$this->updated_bytes = $diff->end;
+
+			foreach ( $this->bookmarks as $name => &$position ) {
+				$update_head = $position->start >= $diff->start;
+				$update_tail = $position->end >= $diff->start;
+
+				if ( ! $update_head && ! $update_tail ) {
+					continue;
+				}
+
+				/*
+				 * If a change is made that encompasses an entire bookmark then we
+				 * have to remove the bookmark as the semantic place it pointed to
+				 * no longer exists. It could seem like we can let it remain as
+				 * long as we haven't removed the text, but if the text is different
+				 * then the place likely doesn't exist at all either and we need to
+				 * start over.
+				 */
+				if ( $diff->start <= $position->start && $diff->end >= $position->end ) {
+					unset( $this->bookmarks[ $name ] );
+					continue;
+				}
+
+				$delta = strlen( $diff->text ) - ( $diff->end - $diff->start );
+
+				if ( $update_head ) {
+					$position->start += $delta;
+				}
+
+				if ( $update_tail ) {
+					$position->end += $delta;
+				}
+			}
 		}
 
 		$this->attribute_updates = array();
 	}
 
+	/**
+	 * Move the current pointer in the Tag Processor to a given bookmark's location.
+	 *
+	 * @param string $bookmark_name Name of bookmark to which to rewind.
+	 * @return bool
+	 * @throws Exception Throws on invalid bookmark name if WP_DEBUG set.
+	 */
+	public function seek( $bookmark_name ) {
+		if ( ! array_key_exists( $bookmark_name, $this->bookmarks ) ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				throw new Exception( 'Invalid bookmark name' );
+			}
+			return false;
+		}
+
+		// Apply all the updates.
+		$this->apply_string_diffs();
+
+		$start               = $this->bookmarks[ $bookmark_name ]->start;
+		$this->parsed_bytes  = $start;
+		$this->updated_bytes = $start;
+		$this->updated_html  = substr( $this->html, 0, $this->parsed_bytes );
+		return $this->next_tag();
+	}
+
+	public function dangerously_get_contents( $start_bookmark, $end_bookmark, $region = 'outer' ) {
+		if (
+			empty( $start_bookmark ) ||
+			empty( $end_bookmark ) ||
+			! isset( $this->bookmarks[ $start_bookmark ], $this->bookmarks[ $end_bookmark ] ) ||
+			( $start_bookmark === $end_bookmark && $region !== 'outer' )
+		) {
+			return false;
+		}
+
+		$start = $this->bookmarks[ $start_bookmark ];
+		$end   = $this->bookmarks[ $end_bookmark ];
+
+		if ( $start->start > $end->start || $start->end > $end->end ) {
+			return false;
+		}
+
+		$start = 'outer' === $region ? $start->start : $start->end + 1;
+		$end   = 'outer' === $region ? $end->end + 1 : $end->start - 1;
+
+		return substr( $this->html, $start, $end - $start );
+	}
+
+	public function dangerously_replace( $start_bookmark, $end_bookmark, $text, $region = 'outer' ) {
+		if (
+			empty( $start_bookmark ) ||
+			empty( $end_bookmark ) ||
+			! isset( $this->bookmarks[ $start_bookmark ], $this->bookmarks[ $end_bookmark ] ) ||
+			( $start_bookmark === $end_bookmark && $region !== 'outer' )
+		) {
+			return false;
+		}
+
+		$start = $this->bookmarks[ $start_bookmark ];
+		$end   = $this->bookmarks[ $end_bookmark ];
+
+		if ( $start->start > $end->start || $start->end > $end->end ) {
+			return false;
+		}
+
+		$start = 'outer' === $region ? $start->start : $start->end + 1;
+		$end   = 'outer' === $region ? $end->end + 1 : $end->start - 1;
+
+		$this->attribute_updates[] = new WP_HTML_Text_Replacement( $start, $end, $text );
+		$this->apply_attributes_updates();
+	}
+
 	/**
 	 * Sort function to arrange objects with a start property in ascending order.
 	 *
@@ -1416,6 +1571,15 @@ public function get_updated_html() {
 			return $this->updated_html . substr( $this->html, $this->updated_bytes );
 		}
 
+		return $this->apply_string_diffs();
+	}
+
+	/**
+	 * I just ripped out the part I need to call in the rewind().
+	 *
+	 * @TODO separate it more cleanly.
+	 */
+	private function apply_string_diffs() {
 		/*
 		 * Parsing is in progress – let's apply the attribute updates without moving on to the next tag.
 		 *
diff --git a/phpunit/html/wp-html-tag-processor-bookmark-test.php b/phpunit/html/wp-html-tag-processor-bookmark-test.php
new file mode 100644
index 00000000000000..b7e05a0a212f91
--- /dev/null
+++ b/phpunit/html/wp-html-tag-processor-bookmark-test.php
@@ -0,0 +1,270 @@
+<?php
+/**
+ * Unit tests covering WP_HTML_Tag_Processor bookmark functionality.
+ *
+ * @package WordPress
+ * @subpackage HTML
+ */
+
+require_once __DIR__ . '/../../lib/experimental/html/index.php';
+
+/**
+ * @group html
+ *
+ * @coversDefaultClass WP_HTML_Tag_Processor
+ */
+class WP_HTML_Tag_Processor_Bookmark_Test extends WP_UnitTestCase {
+	/**
+	 * @ticket 56299
+	 *
+	 * @covers set_bookmark
+	 */
+	public function test_bookmark() {
+		$p = new WP_HTML_Tag_Processor( '<ul><li>One</li><li>Two</li><li>Three</li></ul>' );
+		$p->next_tag( 'li' );
+		$p->set_bookmark( 'first li' );
+		$p->next_tag( 'li' );
+		$p->set_bookmark( 'second li' );
+		$p->set_attribute( 'foo-2', 'bar-2' );
+		$p->seek( 'first li' );
+		$p->set_attribute( 'foo-1', 'bar-1' );
+		$p->seek( 'second li' );
+		$p->next_tag( 'li' );
+		$p->set_attribute( 'foo-3', 'bar-3' );
+		$this->assertEquals(
+			'<ul><li foo-1="bar-1">One</li><li foo-2="bar-2">Two</li><li foo-3="bar-3">Three</li></ul>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_updates_bookmark_for_additions_after_both_sides() {
+		$p = new WP_HTML_Tag_Processor( '<div>First</div><div>Second</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->add_class( 'second' );
+
+		$p->seek( 'first' );
+		$p->add_class( 'first' );
+
+		$this->assertEquals(
+			'<div class="first">First</div><div class="second">Second</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_updates_bookmark_for_additions_before_both_sides() {
+		$p = new WP_HTML_Tag_Processor( '<div>First</div><div>Second</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->set_bookmark( 'second' );
+
+		$p->seek( 'first' );
+		$p->add_class( 'first' );
+
+		$p->seek( 'second' );
+		$p->add_class( 'second' );
+
+		$this->assertEquals(
+			'<div class="first">First</div><div class="second">Second</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_updates_bookmark_for_deletions_after_both_sides() {
+		$p = new WP_HTML_Tag_Processor( '<div>First</div><div disabled>Second</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->remove_attribute( 'disabled' );
+
+		$p->seek( 'first' );
+		$p->set_attribute( 'untouched', true );
+
+		$this->assertEquals(
+			/** @TODO: we shouldn't have to assert the extra space after removing the attribute. */
+			'<div untouched>First</div><div >Second</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_updates_bookmark_for_deletions_before_both_sides() {
+		$p = new WP_HTML_Tag_Processor( '<div disabled>First</div><div>Second</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->set_bookmark( 'second' );
+
+		$p->seek( 'first' );
+		$p->remove_attribute( 'disabled' );
+
+		$p->seek( 'second' );
+		$p->set_attribute( 'safe', true );
+
+		$this->assertEquals(
+			/** @TODO: we shouldn't have to assert the extra space after removing the attribute. */
+			'<div >First</div><div safe>Second</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_replaces_inner_contents() {
+		$p = new WP_HTML_Tag_Processor( '<div class="outer">Before<div class="inner">Inside</div>After</div>' );
+		$p->next_tag( [ 'class_name' => 'inner' ] );
+		$p->set_bookmark( 'start' );
+		$p->next_tag( [ 'tag_name' => 'div', 'tag_closers' => 'visit' ] );
+		$p->set_bookmark( 'end' );
+		$p->dangerously_replace( 'start', 'end', '--', 'inner' );
+
+		$this->assertEquals(
+			'<div class="outer">Before<div class="inner">--</div>After</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_replaces_outside_contents() {
+		$p = new WP_HTML_Tag_Processor( '<div class="outer">Before<div class="inner">Inside</div>After</div>' );
+		$p->next_tag( [ 'class_name' => 'inner' ] );
+		$p->set_bookmark( 'start' );
+		$p->next_tag( [ 'tag_name' => 'div', 'tag_closers' => 'visit' ] );
+		$p->set_bookmark( 'end' );
+		$p->dangerously_replace( 'start', 'end', '--' );
+
+		$this->assertEquals(
+			'<div class="outer">Before--After</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_replaces_single_token() {
+		$p = new WP_HTML_Tag_Processor( 'This is an <img> tag.' );
+		$p->next_tag();
+		$p->set_bookmark( 'image' );
+		$p->dangerously_replace( 'image', 'image', '(image)' );
+
+		$this->assertEquals(
+			'This is an (image) tag.',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_does_nothing_when_replacing_inner_of_single_token() {
+		$p = new WP_HTML_Tag_Processor( 'This is an <img> tag.' );
+		$p->next_tag();
+		$p->set_bookmark( 'image' );
+		$p->dangerously_replace( 'image', 'image', '(image)', 'inner' );
+
+		$this->assertEquals(
+			'This is an <img> tag.',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_does_nothing_when_given_twisted_bookmarks() {
+		$p = new WP_HTML_Tag_Processor( '<div><span></span></div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->set_bookmark( 'second' );
+		$p->dangerously_replace( 'second', 'first', '--' );
+
+		$this->assertEquals(
+			'<div><span></span></div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_bookmarks_deactive_when_bookmarked_token_disappears() {
+		$p = new WP_HTML_Tag_Processor( '<div>Before<div>Inside</div>After</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'first' );
+		$p->next_tag();
+		$p->set_bookmark( 'inner_start' );
+		$p->next_tag( [ 'tag_closers' => 'visit' ] );
+		$p->set_bookmark( 'inner_end' );
+		$p->dangerously_replace( 'first', 'inner_end', '' );
+
+		$this->expectException( Exception::class );
+		$p->seek( 'inner_start' );
+
+		$p->set_attribute( 'wonky', true );
+
+		$this->assertEquals(
+			'After</div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_gets_inner_content() {
+		$p = new WP_HTML_Tag_Processor( '<div>Before<div>Inside</div>After</div>' );
+		$p->next_tag();
+		$p->set_bookmark( 'start' );
+		$p->next_tag( [ 'tag_closers' => 'visit', 'match_offset' => 3 ] );
+		$p->set_bookmark( 'end' );
+
+		$this->assertEquals(
+			'Before<div>Inside</div>After',
+			$p->dangerously_get_contents( 'start', 'end', 'inner' )
+		);
+	}
+
+	public function test_gets_outer_content() {
+		$p = new WP_HTML_Tag_Processor( '<div>Before<div class="start">Inside</div>After</div>' );
+		$p->next_tag( [ 'class_name' => 'start' ] );
+		$p->set_bookmark( 'start' );
+		$p->next_tag( [ 'tag_closers' => 'visit' ] );
+		$p->set_bookmark( 'end' );
+
+		$this->assertEquals(
+			'<div class="start">Inside</div>',
+			$p->dangerously_get_contents( 'start', 'end' )
+		);
+	}
+
+	public function test_can_replace_parent_with_children() {
+		$p = new WP_HTML_Tag_Processor( '<div><h1>Unwrapping HTML</h1><div class="wrapper"><p>Blah blah</p><img></div></div>' );
+		$p->next_tag( [ 'class_name' => 'wrapper' ] );
+		$p->set_bookmark( 'start' );
+		$p->next_tag( [ 'tag_name' => 'div', 'tag_closers' => 'visit' ] );
+		$p->set_bookmark( 'end' );
+
+		$inner_html = $p->dangerously_get_contents( 'start', 'end', 'inner' );
+		$p->dangerously_replace( 'start', 'end', $inner_html, 'outer' );
+
+		$this->assertEquals(
+			'<div><h1>Unwrapping HTML</h1><p>Blah blah</p><img></div>',
+			$p->get_updated_html()
+		);
+	}
+
+	public function test_can_write_dangerous_functions_to_replace_inner_html() {
+		$replace_inner_html = function ( WP_HTML_Tag_Processor $p, $html ) {
+			$tag = $p->get_tag();
+			$p->set_bookmark( '__start_of_node' );
+
+			$depth = 1;
+			while ( $depth > 0 && $p->next_tag( [ 'tag_name' => $tag, 'tag_closers' => 'visit' ] ) ) {
+				$depth += $p->is_tag_closer() ? -1 : 1;
+
+				if ( $depth === 0 ) {
+					$p->set_bookmark( '__end_of_node' );
+					break;
+				}
+			}
+
+			$p->dangerously_replace( '__start_of_node', '__end_of_node', $html, 'inner' );
+			$p->release_bookmark( '__start_of_node' );
+			$p->release_bookmark( '__end_of_node' );
+		};
+
+		$p = new WP_HTML_Tag_Processor( '<div><h1>Unwrapping HTML</h1><div class="wrapper"><p>Blah blah</p><div class="wrapper"><img></div></div><div class="wrapper">untouched</div></div>' );
+		$p->next_tag( [ 'class_name' => 'wrapper' ] );
+
+		$replace_inner_html( $p, '<strong>Weee!</strong>' );
+		$this->assertEquals(
+			'<div><h1>Unwrapping HTML</h1><div class="wrapper"><strong>Weee!</strong></div><div class="wrapper">untouched</div></div>',
+			$p->get_updated_html()
+		);
+	}
+}