diff --git a/src/wp-includes/html-api/class-wp-html-open-elements.php b/src/wp-includes/html-api/class-wp-html-open-elements.php
index aeee107250895..c5d0a7b9fcd30 100644
--- a/src/wp-includes/html-api/class-wp-html-open-elements.php
+++ b/src/wp-includes/html-api/class-wp-html-open-elements.php
@@ -281,6 +281,7 @@ public function has_element_in_specific_scope( string $tag_name, $termination_li
 	 * >   - th
 	 * >   - marquee
 	 * >   - object
+	 * >   - select
 	 * >   - template
 	 * >   - MathML mi
 	 * >   - MathML mo
@@ -312,6 +313,7 @@ public function has_element_in_scope( string $tag_name ): bool {
 				'TH',
 				'MARQUEE',
 				'OBJECT',
+				'SELECT',
 				'TEMPLATE',
 
 				'math MI',
@@ -362,6 +364,7 @@ public function has_element_in_list_item_scope( string $tag_name ): bool {
 				'MARQUEE',
 				'OBJECT',
 				'OL',
+				'SELECT',
 				'TEMPLATE',
 				'UL',
 
@@ -410,6 +413,7 @@ public function has_element_in_button_scope( string $tag_name ): bool {
 				'TH',
 				'MARQUEE',
 				'OBJECT',
+				'SELECT',
 				'TEMPLATE',
 
 				'math MI',
@@ -459,9 +463,8 @@ public function has_element_in_table_scope( string $tag_name ): bool {
 	/**
 	 * Returns whether a particular element is in select scope.
 	 *
-	 * This test differs from the others like it, in that its rules are inverted.
-	 * Instead of arriving at a match when one of any tag in a termination group
-	 * is reached, this one terminates if any other tag is reached.
+	 * The "select scope" concept was removed from the HTML standard along with the
+	 * customizable `<select>` changes, so nothing is ever in select scope.
 	 *
 	 * > The stack of open elements is said to have a particular element in select scope when it has
 	 * > that element in the specific scope consisting of all element types except the following:
@@ -471,24 +474,14 @@ public function has_element_in_table_scope( string $tag_name ): bool {
 	 * @since 6.4.0 Stub implementation (throws).
 	 * @since 6.7.0 Full implementation.
 	 *
-	 * @see https://html.spec.whatwg.org/#has-an-element-in-select-scope
+	 * @deprecated 7.1.0 This method is no longer part of the HTML standard.
+	 * @ignore
 	 *
 	 * @param string $tag_name Name of tag to check.
-	 * @return bool Whether the given element is in SELECT scope.
+	 * @return bool Always false; select scope no longer exists.
 	 */
 	public function has_element_in_select_scope( string $tag_name ): bool {
-		foreach ( $this->walk_up() as $node ) {
-			if ( $node->node_name === $tag_name ) {
-				return true;
-			}
-
-			if (
-				'OPTION' !== $node->node_name &&
-				'OPTGROUP' !== $node->node_name
-			) {
-				return false;
-			}
-		}
+		_deprecated_function( __METHOD__, '7.1.0' );
 
 		return false;
 	}
@@ -697,6 +690,7 @@ public function after_element_push( WP_HTML_Token $item ): void {
 			case 'TH':
 			case 'MARQUEE':
 			case 'OBJECT':
+			case 'SELECT':
 			case 'TEMPLATE':
 			case 'math MI':
 			case 'math MO':
@@ -753,6 +747,7 @@ public function after_element_pop( WP_HTML_Token $item ): void {
 			case 'TH':
 			case 'MARQUEE':
 			case 'OBJECT':
+			case 'SELECT':
 			case 'TEMPLATE':
 			case 'math MI':
 			case 'math MO':
diff --git a/src/wp-includes/html-api/class-wp-html-processor-state.php b/src/wp-includes/html-api/class-wp-html-processor-state.php
index c7c63286e1ebf..d1b3526a9cc79 100644
--- a/src/wp-includes/html-api/class-wp-html-processor-state.php
+++ b/src/wp-includes/html-api/class-wp-html-processor-state.php
@@ -209,7 +209,9 @@ class WP_HTML_Processor_State {
 	 *
 	 * @since 6.7.0
 	 *
-	 * @see https://html.spec.whatwg.org/#parsing-main-inselect
+	 * @deprecated 7.1.0 The "in select" insertion mode was removed from the standard.
+	 * @ignore
+	 *
 	 * @see WP_HTML_Processor_State::$insertion_mode
 	 *
 	 * @var string
@@ -221,7 +223,9 @@ class WP_HTML_Processor_State {
 	 *
 	 * @since 6.7.0
 	 *
-	 * @see https://html.spec.whatwg.org/#parsing-main-inselectintable
+	 * @deprecated 7.1.0 The "in select in table" insertion mode was removed from the standard.
+	 * @ignore
+	 *
 	 * @see WP_HTML_Processor_State::$insertion_mode
 	 *
 	 * @var string
diff --git a/src/wp-includes/html-api/class-wp-html-processor.php b/src/wp-includes/html-api/class-wp-html-processor.php
index 967d616129647..34a8e7b605a06 100644
--- a/src/wp-includes/html-api/class-wp-html-processor.php
+++ b/src/wp-includes/html-api/class-wp-html-processor.php
@@ -121,6 +121,17 @@
  *  - SCRIPT and STYLE tags containing text that looks like HTML but isn't, e.g. `<script>document.write('<p>Hi</p>');</script>`.
  *  - SCRIPT content which has been escaped, e.g. `<script><!-- document.write('<script>console.log("hi")</script>') --></script>`.
  *
+ * ### Customizable select elements
+ *
+ * This parser implements the updated `SELECT` parsing rules introduced by the HTML
+ * standard's customizable select elements changes.
+ *
+ * It does not implement the "maybe clone an option into selectedcontent" step that
+ * copies the selected `OPTION` content into a `SELECTEDCONTENT` element. A
+ * `SELECTEDCONTENT` is otherwise parsed like any other element. In the single case
+ * where producing a correct tree would depend on that cloning, a
+ * `SELECT > BUTTON > SELECTEDCONTENT`, the parser stops processing instead.
+ *
  * ### Unsupported Features
  *
  * This parser does not report parse errors.
@@ -139,6 +150,7 @@
  *
  * @see WP_HTML_Tag_Processor
  * @see https://html.spec.whatwg.org/
+ * @see https://github.com/whatwg/html/pull/10548 Customizable select elements parsing changes.
  * @phpstan-consistent-constructor
  */
 class WP_HTML_Processor extends WP_HTML_Tag_Processor {
@@ -1138,12 +1150,6 @@ public function step( $node_to_process = self::PROCESS_NEXT_NODE ): bool {
 				case WP_HTML_Processor_State::INSERTION_MODE_IN_CELL:
 					return $this->step_in_cell();
 
-				case WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT:
-					return $this->step_in_select();
-
-				case WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT_IN_TABLE:
-					return $this->step_in_select_in_table();
-
 				case WP_HTML_Processor_State::INSERTION_MODE_IN_TEMPLATE:
 					return $this->step_in_template();
 
@@ -2655,7 +2661,7 @@ private function step_in_body(): bool {
 			 * > An end tag whose tag name is one of: "address", "article", "aside", "blockquote",
 			 * > "button", "center", "details", "dialog", "dir", "div", "dl", "fieldset",
 			 * > "figcaption", "figure", "footer", "header", "hgroup", "listing", "main",
-			 * > "menu", "nav", "ol", "pre", "search", "section", "summary", "ul"
+			 * > "menu", "nav", "ol", "pre", "search", "section", "select", "summary", "ul"
 			 */
 			case '-ADDRESS':
 			case '-ARTICLE':
@@ -2682,6 +2688,7 @@ private function step_in_body(): bool {
 			case '-PRE':
 			case '-SEARCH':
 			case '-SECTION':
+			case '-SELECT':
 			case '-SUMMARY':
 			case '-UL':
 				if ( ! $this->state->stack_of_open_elements->has_element_in_scope( $token_name ) ) {
@@ -3000,6 +3007,28 @@ private function step_in_body(): bool {
 			 * > A start tag whose tag name is "input"
 			 */
 			case '+INPUT':
+				/*
+				 * > If the parser was created as part of the HTML fragment parsing algorithm
+				 * > (fragment case) and the context element passed to that algorithm is a
+				 * > select element:
+				 * >   1. Parse error.
+				 * >   2. Ignore the token.
+				 * >   3. Return.
+				 */
+				if ( isset( $this->context_node ) && 'SELECT' === $this->context_node->node_name ) {
+					return $this->step();
+				}
+
+				/*
+				 * > If the stack of open elements has a select element in scope:
+				 * >   1. Parse error.
+				 * >   2. Pop elements from the stack of open elements until a select element
+				 * >      has been popped from the stack.
+				 */
+				if ( $this->state->stack_of_open_elements->has_element_in_scope( 'SELECT' ) ) {
+					$this->state->stack_of_open_elements->pop_until( 'SELECT' );
+				}
+
 				$this->reconstruct_active_formatting_elements();
 				$this->insert_html_element( $this->state->current_token );
 
@@ -3031,6 +3060,17 @@ private function step_in_body(): bool {
 				if ( $this->state->stack_of_open_elements->has_p_in_button_scope() ) {
 					$this->close_a_p_element();
 				}
+
+				if ( $this->state->stack_of_open_elements->has_element_in_scope( 'SELECT' ) ) {
+					$this->generate_implied_end_tags();
+					/*
+					 * > If the stack of open elements has an option element in scope or has
+					 * > an optgroup element in scope, then this is a parse error.
+					 *
+					 * @todo Indicate a parse error once it's possible.
+					 */
+				}
+
 				$this->insert_html_element( $this->state->current_token );
 				$this->state->frameset_ok = false;
 				return true;
@@ -3117,40 +3157,69 @@ private function step_in_body(): bool {
 			 * > A start tag whose tag name is "select"
 			 */
 			case '+SELECT':
+				/*
+				 * > If the parser was created as part of the HTML fragment parsing algorithm
+				 * > (fragment case) and the context element passed to that algorithm is a
+				 * > select element:
+				 * >   1. Parse error.
+				 * >   2. Ignore the token.
+				 */
+				if ( isset( $this->context_node ) && 'SELECT' === $this->context_node->node_name ) {
+					// @todo Indicate a parse error once it's possible.
+					return $this->step();
+				}
+				/*
+				 * > Otherwise, if the stack of open elements has a select element in scope:
+				 * >   1. Parse error.
+				 * >   2. Ignore the token.
+				 * >   3. Pop elements from the stack of open elements until a select element
+				 * >      has been popped from the stack.
+				 */
+				if ( $this->state->stack_of_open_elements->has_element_in_scope( 'SELECT' ) ) {
+					// @todo Indicate a parse error once it's possible.
+					$this->state->stack_of_open_elements->pop_until( 'SELECT' );
+					return $this->step();
+				}
+
 				$this->reconstruct_active_formatting_elements();
 				$this->insert_html_element( $this->state->current_token );
 				$this->state->frameset_ok = false;
+				return true;
 
-				switch ( $this->state->insertion_mode ) {
-					/*
-					 * > If the insertion mode is one of "in table", "in caption", "in table body", "in row",
-					 * > or "in cell", then switch the insertion mode to "in select in table".
-					 */
-					case WP_HTML_Processor_State::INSERTION_MODE_IN_TABLE:
-					case WP_HTML_Processor_State::INSERTION_MODE_IN_CAPTION:
-					case WP_HTML_Processor_State::INSERTION_MODE_IN_TABLE_BODY:
-					case WP_HTML_Processor_State::INSERTION_MODE_IN_ROW:
-					case WP_HTML_Processor_State::INSERTION_MODE_IN_CELL:
-						$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT_IN_TABLE;
-						break;
-
+			/*
+			 * > A start tag whose tag name is "option"
+			 */
+			case '+OPTION':
+				if ( $this->state->stack_of_open_elements->has_element_in_scope( 'SELECT' ) ) {
+					$this->generate_implied_end_tags( 'OPTGROUP' );
 					/*
-					 * > Otherwise, switch the insertion mode to "in select".
+					 * > If the stack of open elements has an option element in scope, then this
+					 * > is a parse error.
+					 * @todo Indicate a parse error once it's possible.
 					 */
-					default:
-						$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT;
-						break;
+				} elseif ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
+					$this->state->stack_of_open_elements->pop();
 				}
+
+				$this->reconstruct_active_formatting_elements();
+				$this->insert_html_element( $this->state->current_token );
 				return true;
 
 			/*
-			 * > A start tag whose tag name is one of: "optgroup", "option"
+			 * > A start tag whose tag name is "optgroup"
 			 */
 			case '+OPTGROUP':
-			case '+OPTION':
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
+				if ( $this->state->stack_of_open_elements->has_element_in_scope( 'SELECT' ) ) {
+					$this->generate_implied_end_tags();
+					/*
+					 * > If the stack of open elements has an option element in scope or has an
+					 * > optgroup element in scope, then this is a parse error.
+					 * @todo Indicate a parse error once it's possible.
+					 */
+				} elseif ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
 					$this->state->stack_of_open_elements->pop();
 				}
+
 				$this->reconstruct_active_formatting_elements();
 				$this->insert_html_element( $this->state->current_token );
 				return true;
@@ -3249,12 +3318,36 @@ private function step_in_body(): bool {
 			/*
 			 * > Any other start tag
 			 */
+
+			/*
+			 * SELECT > BUTTON > SELECTEDCONTENT requires special handling, cloning the
+			 * selected option. This is unsupported.
+			 */
+			if ( 'SELECTEDCONTENT' === $token_name ) {
+				$walker = $this->state->stack_of_open_elements->walk_up();
+				if ( null !== $walker->current() && $walker->current()->node_name === 'BUTTON' ) {
+					$walker->next();
+					if ( null !== $walker->current() && $walker->current()->node_name === 'SELECT' ) {
+						$this->bail( 'Cannot process SELECTEDCONTENT where cloning may be necessary.' );
+					}
+				}
+			}
 			$this->reconstruct_active_formatting_elements();
 			$this->insert_html_element( $this->state->current_token );
 			return true;
 		} else {
 			/*
 			 * > Any other end tag
+			 *
+			 * OPTION end tags are handled here as well:
+			 *
+			 * > An end tag whose tag name is "option"
+			 * >   - Let option be the first option element in the stack of open elements.
+			 * >   - Run the steps for "any other end tag."
+			 * >   - If option is no longer in the stack of open elements, then run maybe clone
+			 * >     an option into selectedcontent given option.
+			 *
+			 * The "maybe clone an option into selectedcontent" algorithm is not implemented.
 			 */
 
 			/*
@@ -4082,247 +4175,6 @@ private function step_in_cell(): bool {
 		return $this->step_in_body();
 	}
 
-	/**
-	 * Parses next element in the 'in select' insertion mode.
-	 *
-	 * This internal function performs the 'in select' insertion mode
-	 * logic for the generalized WP_HTML_Processor::step() function.
-	 *
-	 * @since 6.7.0
-	 * @ignore
-	 *
-	 * @throws WP_HTML_Unsupported_Exception When encountering unsupported HTML input.
-	 *
-	 * @see https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-inselect
-	 * @see WP_HTML_Processor::step
-	 *
-	 * @return bool Whether an element was found.
-	 */
-	private function step_in_select(): bool {
-		$token_name = $this->get_token_name();
-		$token_type = $this->get_token_type();
-		$op_sigil   = '#tag' === $token_type ? ( parent::is_tag_closer() ? '-' : '+' ) : '';
-		$op         = "{$op_sigil}{$token_name}";
-
-		switch ( $op ) {
-			/*
-			 * > Any other character token
-			 */
-			case '#text':
-				/*
-				 * > A character token that is U+0000 NULL
-				 *
-				 * If a text node only comprises null bytes then it should be
-				 * entirely ignored and should not return to calling code.
-				 */
-				if ( parent::TEXT_IS_NULL_SEQUENCE === $this->text_node_classification ) {
-					// Parse error: ignore the token.
-					return $this->step();
-				}
-
-				$this->insert_html_element( $this->state->current_token );
-				return true;
-
-			/*
-			 * > A comment token
-			 */
-			case '#comment':
-			case '#funky-comment':
-			case '#presumptuous-tag':
-				$this->insert_html_element( $this->state->current_token );
-				return true;
-
-			/*
-			 * > A DOCTYPE token
-			 */
-			case 'html':
-				// Parse error: ignore the token.
-				return $this->step();
-
-			/*
-			 * > A start tag whose tag name is "html"
-			 */
-			case '+HTML':
-				return $this->step_in_body();
-
-			/*
-			 * > A start tag whose tag name is "option"
-			 */
-			case '+OPTION':
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
-					$this->state->stack_of_open_elements->pop();
-				}
-				$this->insert_html_element( $this->state->current_token );
-				return true;
-
-			/*
-			 * > A start tag whose tag name is "optgroup"
-			 * > A start tag whose tag name is "hr"
-			 *
-			 * These rules are identical except for the treatment of the self-closing flag and
-			 * the subsequent pop of the HR void element, all of which is handled elsewhere in the processor.
-			 */
-			case '+OPTGROUP':
-			case '+HR':
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
-					$this->state->stack_of_open_elements->pop();
-				}
-
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTGROUP' ) ) {
-					$this->state->stack_of_open_elements->pop();
-				}
-
-				$this->insert_html_element( $this->state->current_token );
-				return true;
-
-			/*
-			 * > An end tag whose tag name is "optgroup"
-			 */
-			case '-OPTGROUP':
-				$current_node = $this->state->stack_of_open_elements->current_node();
-				if ( $current_node && 'OPTION' === $current_node->node_name ) {
-					foreach ( $this->state->stack_of_open_elements->walk_up( $current_node ) as $parent ) {
-						break;
-					}
-					if ( $parent && 'OPTGROUP' === $parent->node_name ) {
-						$this->state->stack_of_open_elements->pop();
-					}
-				}
-
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTGROUP' ) ) {
-					$this->state->stack_of_open_elements->pop();
-					return true;
-				}
-
-				// Parse error: ignore the token.
-				return $this->step();
-
-			/*
-			 * > An end tag whose tag name is "option"
-			 */
-			case '-OPTION':
-				if ( $this->state->stack_of_open_elements->current_node_is( 'OPTION' ) ) {
-					$this->state->stack_of_open_elements->pop();
-					return true;
-				}
-
-				// Parse error: ignore the token.
-				return $this->step();
-
-			/*
-			 * > An end tag whose tag name is "select"
-			 * > A start tag whose tag name is "select"
-			 *
-			 * > It just gets treated like an end tag.
-			 */
-			case '-SELECT':
-			case '+SELECT':
-				if ( ! $this->state->stack_of_open_elements->has_element_in_select_scope( 'SELECT' ) ) {
-					// Parse error: ignore the token.
-					return $this->step();
-				}
-				$this->state->stack_of_open_elements->pop_until( 'SELECT' );
-				$this->reset_insertion_mode_appropriately();
-				return true;
-
-			/*
-			 * > A start tag whose tag name is one of: "input", "keygen", "textarea"
-			 *
-			 * All three of these tags are considered a parse error when found in this insertion mode.
-			 */
-			case '+INPUT':
-			case '+KEYGEN':
-			case '+TEXTAREA':
-				if ( ! $this->state->stack_of_open_elements->has_element_in_select_scope( 'SELECT' ) ) {
-					// Ignore the token.
-					return $this->step();
-				}
-				$this->state->stack_of_open_elements->pop_until( 'SELECT' );
-				$this->reset_insertion_mode_appropriately();
-				return $this->step( self::REPROCESS_CURRENT_NODE );
-
-			/*
-			 * > A start tag whose tag name is one of: "script", "template"
-			 * > An end tag whose tag name is "template"
-			 */
-			case '+SCRIPT':
-			case '+TEMPLATE':
-			case '-TEMPLATE':
-				return $this->step_in_head();
-		}
-
-		/*
-		 * > Anything else
-		 * >   Parse error: ignore the token.
-		 */
-		return $this->step();
-	}
-
-	/**
-	 * Parses next element in the 'in select in table' insertion mode.
-	 *
-	 * This internal function performs the 'in select in table' insertion mode
-	 * logic for the generalized WP_HTML_Processor::step() function.
-	 *
-	 * @since 6.7.0
-	 * @ignore
-	 *
-	 * @throws WP_HTML_Unsupported_Exception When encountering unsupported HTML input.
-	 *
-	 * @see https://html.spec.whatwg.org/#parsing-main-inselectintable
-	 * @see WP_HTML_Processor::step
-	 *
-	 * @return bool Whether an element was found.
-	 */
-	private function step_in_select_in_table(): bool {
-		$token_name = $this->get_token_name();
-		$token_type = $this->get_token_type();
-		$op_sigil   = '#tag' === $token_type ? ( parent::is_tag_closer() ? '-' : '+' ) : '';
-		$op         = "{$op_sigil}{$token_name}";
-
-		switch ( $op ) {
-			/*
-			 * > A start tag whose tag name is one of: "caption", "table", "tbody", "tfoot", "thead", "tr", "td", "th"
-			 */
-			case '+CAPTION':
-			case '+TABLE':
-			case '+TBODY':
-			case '+TFOOT':
-			case '+THEAD':
-			case '+TR':
-			case '+TD':
-			case '+TH':
-				// @todo Indicate a parse error once it's possible.
-				$this->state->stack_of_open_elements->pop_until( 'SELECT' );
-				$this->reset_insertion_mode_appropriately();
-				return $this->step( self::REPROCESS_CURRENT_NODE );
-
-			/*
-			 * > An end tag whose tag name is one of: "caption", "table", "tbody", "tfoot", "thead", "tr", "td", "th"
-			 */
-			case '-CAPTION':
-			case '-TABLE':
-			case '-TBODY':
-			case '-TFOOT':
-			case '-THEAD':
-			case '-TR':
-			case '-TD':
-			case '-TH':
-				// @todo Indicate a parse error once it's possible.
-				if ( ! $this->state->stack_of_open_elements->has_element_in_table_scope( $token_name ) ) {
-					return $this->step();
-				}
-				$this->state->stack_of_open_elements->pop_until( 'SELECT' );
-				$this->reset_insertion_mode_appropriately();
-				return $this->step( self::REPROCESS_CURRENT_NODE );
-		}
-
-		/*
-		 * > Anything else
-		 */
-		return $this->step_in_select();
-	}
-
 	/**
 	 * Parses next element in the 'in template' insertion mode.
 	 *
@@ -5167,12 +5019,6 @@ private function step_in_foreign_content(): bool {
 				case WP_HTML_Processor_State::INSERTION_MODE_IN_CELL:
 					return $this->step_in_cell();
 
-				case WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT:
-					return $this->step_in_select();
-
-				case WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT_IN_TABLE:
-					return $this->step_in_select_in_table();
-
 				case WP_HTML_Processor_State::INSERTION_MODE_IN_TEMPLATE:
 					return $this->step_in_template();
 
@@ -6063,46 +5909,7 @@ private function reset_insertion_mode_appropriately(): void {
 
 			switch ( $node->node_name ) {
 				/*
-				 * > 4. If node is a `select` element, run these substeps:
-				 * >   1. If _last_ is true, jump to the step below labeled done.
-				 * >   2. Let _ancestor_ be _node_.
-				 * >   3. _Loop_: If _ancestor_ is the first node in the stack of open elements,
-				 * >      jump to the step below labeled done.
-				 * >   4. Let ancestor be the node before ancestor in the stack of open elements.
-				 * >   …
-				 * >   7. Jump back to the step labeled _loop_.
-				 * >   8. _Done_: Switch the insertion mode to "in select" and return.
-				 */
-				case 'SELECT':
-					if ( ! $last ) {
-						foreach ( $this->state->stack_of_open_elements->walk_up( $node ) as $ancestor ) {
-							if ( 'html' !== $ancestor->namespace ) {
-								continue;
-							}
-
-							switch ( $ancestor->node_name ) {
-								/*
-								 * > 5. If _ancestor_ is a `template` node, jump to the step below
-								 * >    labeled _done_.
-								 */
-								case 'TEMPLATE':
-									break 2;
-
-								/*
-								 * > 6. If _ancestor_ is a `table` node, switch the insertion mode to
-								 * >    "in select in table" and return.
-								 */
-								case 'TABLE':
-									$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT_IN_TABLE;
-									return;
-							}
-						}
-					}
-					$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_SELECT;
-					return;
-
-				/*
-				 * > 5. If _node_ is a `td` or `th` element and _last_ is false, then switch the
+				 * > 4. If _node_ is a `td` or `th` element and _last_ is false, then switch the
 				 * >    insertion mode to "in cell" and return.
 				 */
 				case 'TD':
@@ -6113,16 +5920,16 @@ private function reset_insertion_mode_appropriately(): void {
 					}
 					break;
 
-					/*
-					* > 6. If _node_ is a `tr` element, then switch the insertion mode to "in row"
-					* >    and return.
-					*/
+				/*
+				* > 5. If _node_ is a `tr` element, then switch the insertion mode to "in row"
+				* >    and return.
+				*/
 				case 'TR':
 					$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_ROW;
 					return;
 
 				/*
-				 * > 7. If _node_ is a `tbody`, `thead`, or `tfoot` element, then switch the
+				 * > 6. If _node_ is a `tbody`, `thead`, or `tfoot` element, then switch the
 				 * >    insertion mode to "in table body" and return.
 				 */
 				case 'TBODY':
@@ -6132,7 +5939,7 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 8. If _node_ is a `caption` element, then switch the insertion mode to
+				 * > 7. If _node_ is a `caption` element, then switch the insertion mode to
 				 * >    "in caption" and return.
 				 */
 				case 'CAPTION':
@@ -6140,7 +5947,7 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 9. If _node_ is a `colgroup` element, then switch the insertion mode to
+				 * > 8. If _node_ is a `colgroup` element, then switch the insertion mode to
 				 * >    "in column group" and return.
 				 */
 				case 'COLGROUP':
@@ -6148,15 +5955,15 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 10. If _node_ is a `table` element, then switch the insertion mode to
-				 * >     "in table" and return.
+				 * > 9. If _node_ is a `table` element, then switch the insertion mode to
+				 * >    "in table" and return.
 				 */
 				case 'TABLE':
 					$this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_TABLE;
 					return;
 
 				/*
-				 * > 11. If _node_ is a `template` element, then switch the insertion mode to the
+				 * > 10. If _node_ is a `template` element, then switch the insertion mode to the
 				 * >     current template insertion mode and return.
 				 */
 				case 'TEMPLATE':
@@ -6164,7 +5971,7 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 12. If _node_ is a `head` element and _last_ is false, then switch the
+				 * > 11. If _node_ is a `head` element and _last_ is false, then switch the
 				 * >     insertion mode to "in head" and return.
 				 */
 				case 'HEAD':
@@ -6175,7 +5982,7 @@ private function reset_insertion_mode_appropriately(): void {
 					break;
 
 				/*
-				 * > 13. If _node_ is a `body` element, then switch the insertion mode to "in body"
+				 * > 12. If _node_ is a `body` element, then switch the insertion mode to "in body"
 				 * >     and return.
 				 */
 				case 'BODY':
@@ -6183,7 +5990,7 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 14. If _node_ is a `frameset` element, then switch the insertion mode to
+				 * > 13. If _node_ is a `frameset` element, then switch the insertion mode to
 				 * >     "in frameset" and return. (fragment case)
 				 */
 				case 'FRAMESET':
@@ -6191,7 +5998,7 @@ private function reset_insertion_mode_appropriately(): void {
 					return;
 
 				/*
-				 * > 15. If _node_ is an `html` element, run these substeps:
+				 * > 14. If _node_ is an `html` element, run these substeps:
 				 * >     1. If the head element pointer is null, switch the insertion mode to
 				 * >        "before head" and return. (fragment case)
 				 * >     2. Otherwise, the head element pointer is not null, switch the insertion
@@ -6206,7 +6013,7 @@ private function reset_insertion_mode_appropriately(): void {
 		}
 
 		/*
-		 * > 16. If _last_ is true, then switch the insertion mode to "in body"
+		 * > 15. If _last_ is true, then switch the insertion mode to "in body"
 		 * >     and return. (fragment case)
 		 *
 		 * This is only reachable if `$last` is true, as per the fragment parsing case.
diff --git a/tests/phpunit/data/html5lib-tests/README.md b/tests/phpunit/data/html5lib-tests/README.md
index be775c8b497b5..18dd099f75bab 100644
--- a/tests/phpunit/data/html5lib-tests/README.md
+++ b/tests/phpunit/data/html5lib-tests/README.md
@@ -13,7 +13,7 @@ The necessary files have been copied to this directory:
 - `tree-construction/*.dat`
 
 The version of these files was taken from the git commit with
-SHA [`a9f44960a9fedf265093d22b2aa3c7ca123727b9`](https://github.com/html5lib/html5lib-tests/commit/a9f44960a9fedf265093d22b2aa3c7ca123727b9).
+SHA [`9fb614afaa42ce8787840f057b32084308e76549`](https://github.com/html5lib/html5lib-tests/commit/9fb614afaa42ce8787840f057b32084308e76549).
 
 ## Updating
 
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/menuitem-element.dat b/tests/phpunit/data/html5lib-tests/tree-construction/menuitem-element.dat
index fb13c3c33b0ab..f7c8e2c3ca74e 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/menuitem-element.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/menuitem-element.dat
@@ -161,13 +161,14 @@
 #data
 <!DOCTYPE html><select><menuitem></select>
 #errors
-33: Stray start tag “menuitem”.
+1:34: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body, select, menuitem.
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
+|       <menuitem>
 
 #data
 <!DOCTYPE html><option><menuitem>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tables01.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tables01.dat
index aa7915ebba7ea..4079888161887 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tables01.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tables01.dat
@@ -100,8 +100,11 @@
 #data
 <table><select><option>3</select></table>
 #errors
-(1,7): expected-doctype-but-got-start-tag
-(1,15): unexpected-start-tag-implies-table-voodoo
+1:1: ERROR: Expected a doctype token
+1:8: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:16: ERROR: Start tag 'option' isn't allowed here. Currently open tags: html, body, table, select.
+1:24: ERROR: Character tokens aren't legal here
+1:25: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body, table, select, option.
 #document
 | <html>
 |   <head>
@@ -114,12 +117,11 @@
 #data
 <table><select><table></table></select></table>
 #errors
-(1,7): expected-doctype-but-got-start-tag
-(1,15): unexpected-start-tag-implies-table-voodoo
-(1,22): unexpected-table-element-start-tag-in-select-in-table
-(1,22): unexpected-start-tag-implies-end-tag
-(1,39): unexpected-end-tag
-(1,47): unexpected-end-tag
+1:1: ERROR: Expected a doctype token
+1:8: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:16: ERROR: Start tag 'table' isn't allowed here. Currently open tags: html, body, table, select.
+1:31: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body.
+1:40: ERROR: End tag 'table' isn't allowed here. Currently open tags: html, body.
 #document
 | <html>
 |   <head>
@@ -131,9 +133,8 @@
 #data
 <table><select></table>
 #errors
-(1,7): expected-doctype-but-got-start-tag
-(1,15): unexpected-start-tag-implies-table-voodoo
-(1,23): unexpected-table-element-end-tag-in-select-in-table
+1:1: ERROR: Expected a doctype token
+1:8: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
 #document
 | <html>
 |   <head>
@@ -144,9 +145,10 @@
 #data
 <table><select><option>A<tr><td>B</td></tr></table>
 #errors
-(1,7): expected-doctype-but-got-start-tag
-(1,15): unexpected-start-tag-implies-table-voodoo
-(1,28): unexpected-table-element-start-tag-in-select-in-table
+1:1: ERROR: Expected a doctype token
+1:8: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:16: ERROR: Start tag 'option' isn't allowed here. Currently open tags: html, body, table, select.
+1:24: ERROR: Character tokens aren't legal here
 #document
 | <html>
 |   <head>
@@ -292,7 +294,6 @@
 1:13: 'svg' tag isn't allowed here. Currently open tags: html, body, div, table.
 1:33: 'select' tag isn't allowed here. Currently open tags: html, body, div, table, svg, foreignobject.
 1:41: 'table' tag isn't allowed here. Currently open tags: html, body, div, table, svg, foreignobject, select.
-1:41: 'table' tag isn't allowed here. Currently open tags: html, body, div, table, svg, foreignobject.
 1:48: 's' tag isn't allowed here. Currently open tags: html, body, div, table.
 1:51: Premature end of file. Currently open tags: html, body, div, table, s.
 #document
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests1.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests1.dat
index e80e64016d919..15d496eb713de 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests1.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests1.dat
@@ -355,19 +355,20 @@ Line1<br>Line2<br>Line3<br>Line4
 #data
 <select><b><option><select><option></b></select>X
 #errors
-(1,8): expected-doctype-but-got-start-tag
-(1,11): unexpected-start-tag-in-select
-(1,27): unexpected-select-in-select
-(1,39): unexpected-end-tag
-(1,48): unexpected-end-tag
+1:1: ERROR: Expected a doctype token
+1:20: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, b, option.
+1:36: ERROR: End tag 'b' isn't allowed here. Currently open tags: html, body, b, select, option.
+1:50: ERROR: Premature end of file. Currently open tags: html, body, b.
 #document
 | <html>
 |   <head>
 |   <body>
 |     <select>
+|       <b>
+|         <option>
+|     <b>
 |       <option>
-|     <option>
-|       "X"
+|     "X"
 
 #data
 <a><table><td><a><table></table><a></tr><a></table><b>X</b>C<a>Y
@@ -1532,18 +1533,19 @@ Line1<br>Line2<br>Line3<br>Line4
 #data
 <select><b><option><select><option></b></select>
 #errors
-(1,8): expected-doctype-but-got-start-tag
-(1,11): unexpected-start-tag-in-select
-(1,27): unexpected-select-in-select
-(1,39): unexpected-end-tag
-(1,48): unexpected-end-tag
+1:1: ERROR: Expected a doctype token
+1:20: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, b, option.
+1:36: ERROR: End tag 'b' isn't allowed here. Currently open tags: html, body, b, select, option.
+1:49: ERROR: Premature end of file. Currently open tags: html, body, b.
 #document
 | <html>
 |   <head>
 |   <body>
 |     <select>
+|       <b>
+|         <option>
+|     <b>
 |       <option>
-|     <option>
 
 #data
 <html><head><title></title><body></body></html>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests10.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests10.dat
index f84e2d546fab6..3b311e4e03cd8 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests10.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests10.dat
@@ -35,20 +35,17 @@
 #data
 <!DOCTYPE html><body><select><svg></svg></select>
 #errors
-(1,34) unexpected-start-tag-in-select
-(1,40) unexpected-end-tag-in-select
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
+|       <svg svg>
 
 #data
 <!DOCTYPE html><body><select><option><svg></svg></option></select>
 #errors
-(1,42) unexpected-start-tag-in-select
-(1,48) unexpected-end-tag-in-select
 #document
 | <!DOCTYPE html>
 | <html>
@@ -56,6 +53,7 @@
 |   <body>
 |     <select>
 |       <option>
+|         <svg svg>
 
 #data
 <!DOCTYPE html><body><table><svg></svg></table>
@@ -261,13 +259,8 @@
 #data
 <!DOCTYPE html><body><table><tr><td><select><svg><g>foo</g><g>bar</g><p>baz</table><p>quux
 #errors
-(1,49) unexpected-start-tag-in-select
-(1,52) unexpected-start-tag-in-select
-(1,59) unexpected-end-tag-in-select
-(1,62) unexpected-start-tag-in-select
-(1,69) unexpected-end-tag-in-select
-(1,72) unexpected-start-tag-in-select
-(1,83) unexpected-table-element-end-tag-in-select-in-table
+1:70: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, tbody, tr, td, select, svg.
+1:76: ERROR: End tag 'table' isn't allowed here. Currently open tags: html, body, table, tbody, tr, td, select.
 #document
 | <!DOCTYPE html>
 | <html>
@@ -278,28 +271,39 @@
 |         <tr>
 |           <td>
 |             <select>
-|               "foobarbaz"
+|               <svg svg>
+|                 <svg g>
+|                   "foo"
+|                 <svg g>
+|                   "bar"
+|               <p>
+|                 "baz"
 |     <p>
 |       "quux"
 
 #data
 <!DOCTYPE html><body><table><select><svg><g>foo</g><g>bar</g><p>baz</table><p>quux
 #errors
-(1,36) unexpected-start-tag-implies-table-voodoo
-(1,41) unexpected-start-tag-in-select
-(1,44) unexpected-start-tag-in-select
-(1,51) unexpected-end-tag-in-select
-(1,54) unexpected-start-tag-in-select
-(1,61) unexpected-end-tag-in-select
-(1,64) unexpected-start-tag-in-select
-(1,75) unexpected-table-element-end-tag-in-select-in-table
+1:29: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:37: ERROR: Start tag 'svg' isn't allowed here. Currently open tags: html, body, table, select.
+1:62: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, select, svg.
+1:62: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, select.
+1:65: ERROR: Character tokens aren't legal here
+1:66: ERROR: Character tokens aren't legal here
+1:67: ERROR: Character tokens aren't legal here
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
-|       "foobarbaz"
+|       <svg svg>
+|         <svg g>
+|           "foo"
+|         <svg g>
+|           "bar"
+|       <p>
+|         "baz"
 |     <table>
 |     <p>
 |       "quux"
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests17.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests17.dat
index e49bcf03142dc..1c472d1dc1eb8 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests17.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests17.dat
@@ -1,9 +1,8 @@
 #data
 <!doctype html><table><tbody><select><tr>
 #errors
-(1,37): unexpected-start-tag-implies-table-voodoo
-(1,41): unexpected-table-element-start-tag-in-select-in-table
-(1,41): eof-in-table
+(1,30): unexpected-start-tag
+(1,42): premature-eof
 #document
 | <!DOCTYPE html>
 | <html>
@@ -17,9 +16,8 @@
 #data
 <!doctype html><table><tr><select><td>
 #errors
-(1,34): unexpected-start-tag-implies-table-voodoo
-(1,38): unexpected-table-element-start-tag-in-select-in-table
-(1,38): expected-closing-tag-but-got-eof
+(1,27): unexpected-start-tag
+(1,39): premature-eof
 #document
 | <!DOCTYPE html>
 | <html>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests18.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests18.dat
index 0b6d5dc404a9d..a3bb69a16ef57 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests18.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests18.dat
@@ -227,34 +227,42 @@
 #data
 <!doctype html><select><plaintext></plaintext>X
 #errors
-34: Stray start tag “plaintext”.
-46: Stray end tag “plaintext”.
-47: End of file seen and there were open elements.
+1:48: ERROR: Premature end of file. Currently open tags: html, body, select, plaintext.
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
-|       "X"
+|       <plaintext>
+|         "</plaintext>X"
 
 #data
 <!doctype html><table><select><plaintext>a<caption>b
 #errors
-30: Start tag “select” seen in “table”.
-41: Stray start tag “plaintext”.
-51: “caption” start tag with “select” open.
-52: End of file seen and there were open elements.
+1:23: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:31: ERROR: Start tag 'plaintext' isn't allowed here. Currently open tags: html, body, table, select.
+1:42: ERROR: Character tokens aren't legal here
+1:43: ERROR: Character tokens aren't legal here
+1:44: ERROR: Character tokens aren't legal here
+1:45: ERROR: Character tokens aren't legal here
+1:46: ERROR: Character tokens aren't legal here
+1:47: ERROR: Character tokens aren't legal here
+1:48: ERROR: Character tokens aren't legal here
+1:49: ERROR: Character tokens aren't legal here
+1:50: ERROR: Character tokens aren't legal here
+1:51: ERROR: Character tokens aren't legal here
+1:52: ERROR: Character tokens aren't legal here
+1:53: ERROR: Premature end of file. Currently open tags: html, body, table, select, plaintext.
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
-|       "a"
+|       <plaintext>
+|         "a<caption>b"
 |     <table>
-|       <caption>
-|         "b"
 
 #data
 <!doctype html><template><plaintext>a</template>b
@@ -446,8 +454,11 @@
 #data
 <!doctype html><table><select><script></style></script>abc
 #errors
-(1,30): unexpected-start-tag-implies-table-voodoo
-(1,58): eof-in-select
+1:23: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:56: ERROR: Character tokens aren't legal here
+1:57: ERROR: Character tokens aren't legal here
+1:58: ERROR: Character tokens aren't legal here
+1:59: ERROR: Premature end of file. Currently open tags: html, body, table, select.
 #document
 | <!DOCTYPE html>
 | <html>
@@ -462,8 +473,11 @@
 #data
 <!doctype html><table><tr><select><script></style></script>abc
 #errors
-(1,34): unexpected-start-tag-implies-table-voodoo
-(1,62): eof-in-select
+1:27: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table, tbody, tr.
+1:60: ERROR: Character tokens aren't legal here
+1:61: ERROR: Character tokens aren't legal here
+1:62: ERROR: Character tokens aren't legal here
+1:63: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, select.
 #document
 | <!DOCTYPE html>
 | <html>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests2.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests2.dat
index 11ef9b1643ff4..9232edde30918 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests2.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests2.dat
@@ -500,7 +500,7 @@
 #data
 <!DOCTYPE html><select><optgroup><option></optgroup><option><select><option>
 #errors
-(1,68): unexpected-select-in-select
+1:61: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, option.
 #document
 | <!DOCTYPE html>
 | <html>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests7.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests7.dat
index b2db4de1f3bdf..aa7e16b408e2e 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests7.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests7.dat
@@ -200,7 +200,7 @@ X</listing>
 #data
 <!doctype html><select><input>X
 #errors
-(1,30): unexpected-input-in-select
+1:32: ERROR: Premature end of file. Currently open tags: html, body, select.
 #document
 | <!DOCTYPE html>
 | <html>
@@ -213,7 +213,7 @@ X</listing>
 #data
 <!doctype html><select><select>X
 #errors
-(1,31): unexpected-select-in-select
+1:24: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select.
 #document
 | <!DOCTYPE html>
 | <html>
@@ -443,11 +443,11 @@ A<table><tr> B</tr> </em>C</table>
 #data
 <select><keygen>
 #errors
-(1,8): expected-doctype-but-got-start-tag
-(1,16): unexpected-input-in-select
+1:1: ERROR: Expected a doctype token
+1:17: ERROR: Premature end of file. Currently open tags: html, body, select.
 #document
 | <html>
 |   <head>
 |   <body>
 |     <select>
-|     <keygen>
+|       <keygen>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests9.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests9.dat
index f8d04b23bc0be..1456324ffc21f 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests9.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests9.dat
@@ -48,20 +48,17 @@
 #data
 <!DOCTYPE html><body><select><math></math></select>
 #errors
-(1,35) unexpected-start-tag-in-select
-(1,42) unexpected-end-tag-in-select
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
+|       <math math>
 
 #data
 <!DOCTYPE html><body><select><option><math></math></option></select>
 #errors
-(1,43) unexpected-start-tag-in-select
-(1,50) unexpected-end-tag-in-select
 #document
 | <!DOCTYPE html>
 | <html>
@@ -69,6 +66,7 @@
 |   <body>
 |     <select>
 |       <option>
+|         <math math>
 
 #data
 <!DOCTYPE html><body><table><math></math></table>
@@ -301,13 +299,8 @@
 #data
 <!DOCTYPE html><body><table><tr><td><select><math><mi>foo</mi><mi>bar</mi><p>baz</table><p>quux
 #errors
-(1,50) unexpected-start-tag-in-select
-(1,54) unexpected-start-tag-in-select
-(1,62) unexpected-end-tag-in-select
-(1,66) unexpected-start-tag-in-select
-(1,74) unexpected-end-tag-in-select
-(1,77) unexpected-start-tag-in-select
-(1,88) unexpected-table-element-end-tag-in-select-in-table
+1:75: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, tbody, tr, td, select, math.
+1:81: ERROR: End tag 'table' isn't allowed here. Currently open tags: html, body, table, tbody, tr, td, select.
 #document
 | <!DOCTYPE html>
 | <html>
@@ -318,28 +311,45 @@
 |         <tr>
 |           <td>
 |             <select>
-|               "foobarbaz"
+|               <math math>
+|                 <math mi>
+|                   "foo"
+|                 <math mi>
+|                   "bar"
+|               <p>
+|                 "baz"
 |     <p>
 |       "quux"
 
 #data
 <!DOCTYPE html><body><table><select><math><mi>foo</mi><mi>bar</mi><p>baz</table><p>quux
 #errors
-(1,36) unexpected-start-tag-implies-table-voodoo
-(1,42) unexpected-start-tag-in-select
-(1,46) unexpected-start-tag-in-select
-(1,54) unexpected-end-tag-in-select
-(1,58) unexpected-start-tag-in-select
-(1,66) unexpected-end-tag-in-select
-(1,69) unexpected-start-tag-in-select
-(1,80) unexpected-table-element-end-tag-in-select-in-table
+1:29: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, table.
+1:37: ERROR: Start tag 'math' isn't allowed here. Currently open tags: html, body, table, select.
+1:47: ERROR: Character tokens aren't legal here
+1:48: ERROR: Character tokens aren't legal here
+1:49: ERROR: Character tokens aren't legal here
+1:59: ERROR: Character tokens aren't legal here
+1:60: ERROR: Character tokens aren't legal here
+1:61: ERROR: Character tokens aren't legal here
+1:67: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, select, math.
+1:67: ERROR: Start tag 'p' isn't allowed here. Currently open tags: html, body, table, select.
+1:70: ERROR: Character tokens aren't legal here
+1:71: ERROR: Character tokens aren't legal here
+1:72: ERROR: Character tokens aren't legal here
 #document
 | <!DOCTYPE html>
 | <html>
 |   <head>
 |   <body>
 |     <select>
-|       "foobarbaz"
+|       <math math>
+|         <math mi>
+|           "foo"
+|         <math mi>
+|           "bar"
+|       <p>
+|         "baz"
 |     <table>
 |     <p>
 |       "quux"
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/tests_innerHTML_1.dat b/tests/phpunit/data/html5lib-tests/tree-construction/tests_innerHTML_1.dat
index 1a37ee520ae34..09e0456f0f12d 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/tests_innerHTML_1.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/tests_innerHTML_1.dat
@@ -790,7 +790,7 @@ select
 #data
 <input><option>
 #errors
-(1,7): unexpected-input-in-select
+(1,7): XXX-undefined-error
 #document-fragment
 select
 #document
@@ -799,20 +799,21 @@ select
 #data
 <keygen><option>
 #errors
-(1,8): unexpected-input-in-select
 #document-fragment
 select
 #document
+| <keygen>
 | <option>
 
 #data
 <textarea><option>
 #errors
-(1,10): unexpected-input-in-select
+1:19: ERROR: Premature end of file. Currently open tags: html, textarea.
 #document-fragment
 select
 #document
-| <option>
+| <textarea>
+|   "<option>"
 
 #data
 </html><!--abc-->
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/void-in-phrasing.dat b/tests/phpunit/data/html5lib-tests/tree-construction/void-in-phrasing.dat
new file mode 100644
index 0000000000000..b7dbd1e7cec2a
--- /dev/null
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/void-in-phrasing.dat
@@ -0,0 +1,151 @@
+#data
+<!DOCTYPE html><body><p><br></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <br>
+
+#data
+<!DOCTYPE html><body><p><br>text</p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <br>
+|       "text"
+
+#data
+<!DOCTYPE html><body><p>before<br>after</p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       "before"
+|       <br>
+|       "after"
+
+#data
+<!DOCTYPE html><body><p><br><br></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <br>
+|       <br>
+
+#data
+<!DOCTYPE html><body><p>a<br>b<br>c</p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       "a"
+|       <br>
+|       "b"
+|       <br>
+|       "c"
+
+#data
+<!DOCTYPE html><body><h1><br></h1>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <h1>
+|       <br>
+
+#data
+<!DOCTYPE html><body><p><input></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <input>
+
+#data
+<!DOCTYPE html><body><p><img></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <img>
+
+#data
+<!DOCTYPE html><body><p><wbr></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <wbr>
+
+#data
+<!DOCTYPE html><body><p><embed></p>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <p>
+|       <embed>
+
+#data
+<!DOCTYPE html><body><h2><input></h2>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <h2>
+|       <input>
+
+#data
+<!DOCTYPE html><body><em><br></em>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <em>
+|       <br>
+
+#data
+<!DOCTYPE html><body><strong><br>text</strong>
+#errors
+#document
+| <!DOCTYPE html>
+| <html>
+|   <head>
+|   <body>
+|     <strong>
+|       <br>
+|       "text"
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/webkit01.dat b/tests/phpunit/data/html5lib-tests/tree-construction/webkit01.dat
index d30e12e52766e..fc7f5c80e07e4 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/webkit01.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/webkit01.dat
@@ -437,11 +437,11 @@ no-doctype
 #data
 <select><option>A<select><option>B<select><option>C<select><option>D<select><option>E<select><option>F<select><option>G<select>
 #errors
-(1,8): expected-doctype-but-got-start-tag
-(1,25): unexpected-select-in-select
-(1,59): unexpected-select-in-select
-(1,93): unexpected-select-in-select
-(1,127): unexpected-select-in-select
+1:1: ERROR: Expected a doctype token
+1:18: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, option.
+1:52: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, option.
+1:86: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, option.
+1:120: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, option.
 #document
 | <html>
 |   <head>
@@ -528,12 +528,11 @@ no-doctype
 #data
 <kbd><table></kbd><col><select><tr>
 #errors
-(1,5): expected-doctype-but-got-start-tag
-(1,18): unexpected-end-tag-implies-table-voodoo
-(1,18): unexpected-end-tag
-(1,31): unexpected-start-tag-implies-table-voodoo
-(1,35): unexpected-table-element-start-tag-in-select-in-table
-(1,35): eof-in-table
+1:1: ERROR: Expected a doctype token
+1:13: ERROR: End tag 'kbd' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:13: ERROR: End tag 'kbd' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:24: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:36: ERROR: Premature end of file. Currently open tags: html, body, kbd, table, tbody, tr.
 #document
 | <html>
 |   <head>
@@ -549,12 +548,11 @@ no-doctype
 #data
 <kbd><table></kbd><col><select><tr></table><div>
 #errors
-(1,5): expected-doctype-but-got-start-tag
-(1,18): unexpected-end-tag-implies-table-voodoo
-(1,18): unexpected-end-tag
-(1,31): unexpected-start-tag-implies-table-voodoo
-(1,35): unexpected-table-element-start-tag-in-select-in-table
-(1,48): expected-closing-tag-but-got-eof
+1:1: ERROR: Expected a doctype token
+1:13: ERROR: End tag 'kbd' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:13: ERROR: End tag 'kbd' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:24: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, kbd, table.
+1:49: ERROR: Premature end of file. Currently open tags: html, body, kbd, div.
 #document
 | <html>
 |   <head>
diff --git a/tests/phpunit/data/html5lib-tests/tree-construction/webkit02.dat b/tests/phpunit/data/html5lib-tests/tree-construction/webkit02.dat
index 7d817ec69a700..47a3c5713ea86 100644
--- a/tests/phpunit/data/html5lib-tests/tree-construction/webkit02.dat
+++ b/tests/phpunit/data/html5lib-tests/tree-construction/webkit02.dat
@@ -309,12 +309,13 @@ div
 #data
 <option><XH<optgroup></optgroup>
 #errors
-(1,21): unexpected-start-tag-in-select
-(1,32): unexpected-end-tag-in-select
+1:22: ERROR: End tag 'optgroup' isn't allowed here. Currently open tags: html, option, xh<optgroup.
+1:33: ERROR: Premature end of file. Currently open tags: html, option, xh<optgroup.
 #document-fragment
 select
 #document
 | <option>
+|   <xh<optgroup>
 
 #data
 <svg><foreignObject><div>foo</div><plaintext></foreignObject></svg><div>bar</div>
@@ -444,7 +445,7 @@ eof-in-math
 <select><optgroup><hr>
 #errors
 1:1: ERROR: Expected a doctype token
-1:23: ERROR: Premature end of file. Currently open tags: html, body, select.
+1:23: ERROR: Premature end of file. Currently open tags: html, body, select, optgroup.
 #document
 | <html>
 |   <head>
@@ -457,7 +458,7 @@ eof-in-math
 <select><option><optgroup><hr>
 #errors
 1:1: ERROR: Expected a doctype token
-1:31: ERROR: Premature end of file. Currently open tags: html, body, select.
+1:31: ERROR: Premature end of file. Currently open tags: html, body, select, optgroup.
 #document
 | <html>
 |   <head>
@@ -504,7 +505,7 @@ eof-in-math
 <table><tr><td><select><optgroup><option><hr>
 #errors
 1:1: ERROR: Expected a doctype token
-1:46: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select.
+1:46: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select, optgroup.
 #document
 | <html>
 |   <head>
@@ -522,7 +523,7 @@ eof-in-math
 <table><tr><td><select><optgroup><hr>
 #errors
 1:1: ERROR: Expected a doctype token
-1:38: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select.
+1:38: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select, optgroup.
 #document
 | <html>
 |   <head>
@@ -539,7 +540,7 @@ eof-in-math
 <table><tr><td><select><option><optgroup><hr>
 #errors
 1:1: ERROR: Expected a doctype token
-1:46: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select.
+1:38: ERROR: Premature end of file. Currently open tags: html, body, table, tbody, tr, td, select, optgroup.
 #document
 | <html>
 |   <head>
@@ -552,3 +553,223 @@ eof-in-math
 |               <option>
 |               <optgroup>
 |               <hr>
+
+#data
+<select><div><i></div><option>option
+#errors
+1:1: ERROR: Expected a doctype token
+1:17: ERROR: End tag 'div' isn't allowed here. Currently open tags: html, body, select, div, i.
+1:37: ERROR: Premature end of file. Currently open tags: html, body, select, option, i.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <div>
+|         <i>
+|       <i>
+|         <option>
+|           "option"
+
+#data
+<div><i></div><option>option
+#errors
+1:1: ERROR: Expected a doctype token
+1:9: ERROR: End tag 'div' isn't allowed here. Currently open tags: html, body, div, i.
+1:29: ERROR: Premature end of file. Currently open tags: html, body, i, option.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <div>
+|       <i>
+|     <i>
+|       <option>
+|         "option"
+
+#data
+<select><div>div 1</div><button>button</button><div>div 2</div><datalist><option>option</option></datalist><div>div 3</div></select>
+#errors
+1:1: ERROR: Expected a doctype token
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <div>
+|         "div 1"
+|       <button>
+|         "button"
+|       <div>
+|         "div 2"
+|       <datalist>
+|         <option>
+|           "option"
+|       <div>
+|         "div 3"
+
+#data
+<select><button>button</select>
+#errors
+1:1: ERROR: Expected a doctype token
+1:23: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body, select, button.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         "button"
+
+#data
+<select><datalist>datalist</select>
+#errors
+1:1: ERROR: Expected a doctype token
+1:27: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body, select, datalist.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <datalist>
+|         "datalist"
+
+#data
+<select><button><select></select></button></select>
+#errors
+1:1: ERROR: Expected a doctype token
+1:17: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, button.
+1:25: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body.
+1:34: ERROR: End tag 'button' isn't allowed here. Currently open tags: html, body.
+1:43: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+
+#data
+<select><button><div><select></select>
+#errors
+1:1: ERROR: Expected a doctype token
+1:22: ERROR: Start tag 'select' isn't allowed here. Currently open tags: html, body, select, button, div.
+1:30: ERROR: End tag 'select' isn't allowed here. Currently open tags: html, body.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         <div>
+
+#data
+<select><div><option><img>option</option></div></select>
+#errors
+1:1: ERROR: Expected a doctype token
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <div>
+|         <option>
+|           <img>
+|           "option"
+
+#data
+<select><input>
+#errors
+1:1: ERROR: Expected a doctype token
+1:16: ERROR: Premature end of file. Currently open tags: html, body, select.
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|     <input>
+
+#data
+<select><button><selectedcontent></button><option>X
+#errors
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         <selectedcontent>
+|           "X"
+|       <option>
+|         "X"
+
+#data
+<select><button><selectedcontent></button><option>x<i>i<b>ib</i>b
+#errors
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         <selectedcontent>
+|           "x"
+|           <i>
+|             "i"
+|             <b>
+|               "ib"
+|           <b>
+|             "b"
+|       <option>
+|         "x"
+|         <i>
+|           "i"
+|           <b>
+|             "ib"
+|         <b>
+|           "b"
+
+#data
+<select><button><selectedcontent></button><option>X<option>Y
+#errors
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         <selectedcontent>
+|           "X"
+|       <option>
+|         "X"
+|       <option>
+|         "Y"
+
+#data
+<select><button><selectedcontent></button><option>X<option selected>Y
+#errors
+#document
+| <html>
+|   <head>
+|   <body>
+|     <select>
+|       <button>
+|         <selectedcontent>
+|           "Y"
+|       <option>
+|         "X"
+|       <option>
+|         selected=""
+|         "Y"
+
+#data
+<font><select><option>a</option></font></select>
+#errors
+#document
+| <html>
+|   <head>
+|   <body>
+|     <font>
+|       <select>
+|         <option>
+|           "a"