WordPress · AceMedia · Jul 28, 2026
diff --git a/src/wp-includes/block-template.php b/src/wp-includes/block-template.php
@@ -233,6 +233,50 @@ function _block_template_render_title_tag() {
 	echo '<title>' . wp_get_document_title() . '</title>' . "\n";
 }
 
+/**
+ * Prints the opening of the document a block theme renders into.
+ *
+ * Block themes have no header.php, so the markup that opens their documents lives in the
+ * template canvas rather than in the theme. Printing it from here lets anything that has to
+ * open a document on a block theme's behalf produce exactly what the canvas produces.
+ *
+ * @since 7.1.0
+ * @access private
+ */
+function _wp_block_theme_document_start() {
+	echo '<!DOCTYPE html>' . "\n";
+	echo '<html ';
+	language_attributes();
+	echo ">\n";
+	echo "<head>\n";
+	echo "\t" . '<meta charset="';
+	bloginfo( 'charset' );
+	echo '" />' . "\n";
+	echo "\t";
+	wp_head();
+	echo "</head>\n";
+	echo "\n";
+	echo '<body ';
+	body_class();
+	echo ">\n";
+	wp_body_open();
+}
+
+/**
+ * Prints the closing of the document a block theme renders into.
+ *
+ * The counterpart to _wp_block_theme_document_start().
+ *
+ * @since 7.1.0
+ * @access private
+ */
+function _wp_block_theme_document_end() {
+	echo "\n";
+	wp_footer();
+	echo "</body>\n";
+	echo "</html>\n";
+}
+
 /**
  * Returns the markup for the current template.
  *

diff --git a/src/wp-includes/general-template.php b/src/wp-includes/general-template.php
@@ -45,6 +45,19 @@ function get_header( $name = null, $args = array() ) {
 
 	$templates[] = 'header.php';
 
+	/*
+	 * A block theme has no header.php by design, so locate_template() falls through to
+	 * wp-includes/theme-compat/header.php: markup deprecated since 3.0.0 that opens the
+	 * document with the old default theme's page frame and its site title and description.
+	 * Print the same document opening the template canvas uses instead, so a block theme
+	 * gets its own markup whether the page is rendered by a block template or by a caller
+	 * of this function.
+	 */
+	if ( wp_is_block_theme() && ! _wp_theme_has_template( $templates ) ) {
+		_wp_block_theme_document_start();
+		return;
+	}
+
 	if ( ! locate_template( $templates, true, true, $args ) ) {
 		return false;
 	}
@@ -89,6 +102,12 @@ function get_footer( $name = null, $args = array() ) {
 
 	$templates[] = 'footer.php';
 
+	// See get_header(): block themes close their document the way the canvas does.
+	if ( wp_is_block_theme() && ! _wp_theme_has_template( $templates ) ) {
+		_wp_block_theme_document_end();
+		return;
+	}
+
 	if ( ! locate_template( $templates, true, true, $args ) ) {
 		return false;
 	}

diff --git a/src/wp-includes/template-canvas.php b/src/wp-includes/template-canvas.php
@@ -10,18 +10,10 @@
  * This needs to run before <head> so that blocks can add scripts and styles in wp_head().
  */
 $template_html = get_the_block_template_html();
-?><!DOCTYPE html>
-<html <?php language_attributes(); ?>>
-<head>
-	<meta charset="<?php bloginfo( 'charset' ); ?>" />
-	<?php wp_head(); ?>
-</head>
 
-<body <?php body_class(); ?>>
-<?php wp_body_open(); ?>
+_wp_block_theme_document_start();
+?>
 
 <?php echo $template_html; ?>
-
-<?php wp_footer(); ?>
-</body>
-</html>
+<?php
+_wp_block_theme_document_end();
diff --git a/src/wp-includes/template.php b/src/wp-includes/template.php
@@ -752,6 +752,40 @@ function locate_template( $template_names, $load = false, $load_once = true, $ar
 	return $located;
 }
 
+/**
+ * Determines whether the active theme provides one of the given template files.
+ *
+ * Unlike locate_template(), this ignores the deprecated fallbacks in wp-includes/theme-compat/,
+ * so a caller can tell a template the theme actually ships from one of those.
+ *
+ * @since 7.1.0
+ * @access private
+ *
+ * @param string[] $template_names Template file names to look for, in order of priority.
+ * @return bool Whether the theme, or its parent, provides one of the templates.
+ */
+function _wp_theme_has_template( $template_names ) {
+	$stylesheet_path = get_stylesheet_directory();
+	$template_path   = get_template_directory();
+	$is_child_theme  = $stylesheet_path !== $template_path;
+
+	foreach ( (array) $template_names as $template_name ) {
+		if ( ! $template_name ) {
+			continue;
+		}
+
+		if ( file_exists( $stylesheet_path . '/' . $template_name ) ) {
+			return true;
+		}
+
+		if ( $is_child_theme && file_exists( $template_path . '/' . $template_name ) ) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
 /**
  * Requires the template file with WordPress environment.
  *

diff --git a/tests/phpunit/tests/general/template.php b/tests/phpunit/tests/general/template.php
@@ -749,6 +749,83 @@ public function test_get_footer_returns_nothing_on_success() {
 		$this->assertNull( get_footer() );
 	}
 
+	/**
+	 * Tests that a block theme opens its own document rather than the deprecated fallback.
+	 *
+	 * A block theme ships no header.php, so locate_template() reaches
+	 * wp-includes/theme-compat/header.php, whose markup opens the page with the old default
+	 * theme's frame, site title and description.
+	 *
+	 * @ticket 55023
+	 *
+	 * @covers ::get_header
+	 */
+	public function test_get_header_uses_block_theme_document_when_theme_has_no_header() {
+		switch_theme( 'block-theme' );
+
+		$output = get_echo( 'get_header' );
+
+		$this->assertStringContainsString( '<!DOCTYPE html>', $output, 'The document should be opened.' );
+		$this->assertStringContainsString( '<body', $output, 'The body element should be opened.' );
+		$this->assertStringNotContainsString( 'id="page"', $output, 'The theme-compat page frame should not be printed.' );
+		$this->assertStringNotContainsString( 'id="header"', $output, 'The theme-compat header should not be printed.' );
+	}
+
+	/**
+	 * Tests that a block theme closes the document it opened.
+	 *
+	 * @ticket 55023
+	 *
+	 * @covers ::get_footer
+	 */
+	public function test_get_footer_uses_block_theme_document_when_theme_has_no_footer() {
+		switch_theme( 'block-theme' );
+
+		// As a page does: wp_head() is where the back-compat skip link action is unhooked.
+		get_echo( 'get_header' );
+		$output = get_echo( 'get_footer' );
+
+		$this->assertStringContainsString( '</body>', $output, 'The body element should be closed.' );
+		$this->assertStringContainsString( '</html>', $output, 'The document should be closed.' );
+		$this->assertStringNotContainsString( 'proudly powered by', $output, 'The theme-compat footer should not be printed.' );
+		$this->assertStringNotContainsString( 'id="footer"', $output, 'The theme-compat footer should not be printed.' );
+	}
+
+	/**
+	 * Tests that the deprecation notice for a missing header.php is not raised for block themes,
+	 * which are not expected to provide one.
+	 *
+	 * @ticket 55023
+	 *
+	 * @covers ::get_header
+	 */
+	public function test_get_header_does_not_deprecate_for_block_theme() {
+		switch_theme( 'block-theme' );
+
+		// Would trigger the deprecation notice handled by WP_UnitTestCase and fail the test.
+		get_echo( 'get_header' );
+
+		$this->assertTrue( wp_is_block_theme(), 'The test should run on a block theme.' );
+	}
+
+	/**
+	 * Tests that a classic theme without header.php keeps the deprecated fallback, so themes
+	 * relying on it are unaffected. camelCase is a classic fixture theme with no header.php.
+	 *
+	 * @ticket 55023
+	 *
+	 * @expectedDeprecated Theme without header.php
+	 *
+	 * @covers ::get_header
+	 */
+	public function test_get_header_still_falls_back_for_classic_theme() {
+		switch_theme( 'camelCase' );
+
+		$output = get_echo( 'get_header' );
+
+		$this->assertStringContainsString( 'id="page"', $output, 'The theme-compat markup should still be printed for classic themes.' );
+	}
+
 	/**
 	 * @ticket 40969
 	 *