property is modified, the old one is removed and the new one is added
	 * at the end of the list.
	 *
	 * @since 6.5.0
	 *
	 * Example:
	 *
	 *     merge_style_property( 'color:green;', 'color', 'red' )      => 'color:red;'
	 *     merge_style_property( 'background:green;', 'color', 'red' ) => 'background:green;color:red;'
	 *     merge_style_property( 'color:green;', 'color', null )       => ''
	 *
	 * @param string            $style_attribute_value The current style attribute value.
	 * @param string            $style_property_name   The style property name to set.
	 * @param string|false|null $style_property_value  The value to set for the style property. With false, null or an
	 *                                                 empty string, it removes the style property.
	 * @return string The new style attribute value after the specified property has been added, updated or removed.
	 */
	private function merge_style_property( string $style_attribute_value, string $style_property_name, $style_property_value ): string {
		$style_assignments    = explode( ';', $style_attribute_value );
		$result               = array();
		$style_property_value = ! empty( $style_property_value ) ? rtrim( trim( $style_property_value ), ';' ) : null;
		$new_style_property   = $style_property_value ? $style_property_name . ':' . $style_property_value . ';' : '';

		// Generates an array with all the properties but the modified one.
		foreach ( $style_assignments as $style_assignment ) {
			if ( empty( trim( $style_assignment ) ) ) {
				continue;
			}
			list( $name, $value ) = explode( ':', $style_assignment );
			if ( trim( $name ) !== $style_property_name ) {
				$result[] = trim( $name ) . ':' . trim( $value ) . ';';
			}
		}

		// Adds the new/modified property at the end of the list.
		$result[] = $new_style_property;

		return implode( '', $result );
	}

	/**
	 * Processes the `data-wp-text` directive.
	 *
	 * It updates the inner content of the current HTML element based on the
	 * evaluation of its associated reference.
	 *
	 * @since 6.5.0
	 *
	 * @param WP_Interactivity_API_Directives_Processor $p               The directives processor instance.
	 * @param string                                    $mode            Whether the processing is entering or exiting the tag.
	 */
	private function data_wp_text_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ) {
		if ( 'enter' === $mode ) {
			$attribute_value = $p->get_attribute( 'data-wp-text' );
			$result          = $this->evaluate( $attribute_value );

			/*
			 * Follows the same logic as Preact in the client and only changes the
			 * content if the value is a string or a number. Otherwise, it removes the
			 * content.
			 */
			if ( is_string( $result ) || is_numeric( $result ) ) {
				$p->set_content_between_balanced_tags( esc_html( $result ) );
			} else {
				$p->set_content_between_balanced_tags( '' );
			}
		}
	}

	/**
	 * Returns the CSS styles for animating the top loading bar in the router.
	 *
	 * @since 6.5.0
	 *
	 * @return string The CSS styles for the router's top loading bar animation.
	 */
	private function get_router_animation_styles(): string {
		return <<<CSS
			.wp-interactivity-router-loading-bar {
				position: fixed;
				top: 0;
				left: 0;
				margin: 0;
				padding: 0;
				width: 100vw;
				max-width: 100vw !important;
				height: 4px;
				background-color: #000;
				opacity: 0
			}
			.wp-interactivity-router-loading-bar.start-animation {
				animation: wp-interactivity-router-loading-bar-start-animation 30s cubic-bezier(0.03, 0.5, 0, 1) forwards
			}
			.wp-interactivity-router-loading-bar.finish-animation {
				animation: wp-interactivity-router-loading-bar-finish-animation 300ms ease-in
			}
			@keyframes wp-interactivity-router-loading-bar-start-animation {
				0% { transform: scaleX(0); transform-origin: 0 0; opacity: 1 }
				100% { transform: scaleX(1); transform-origin: 0 0; opacity: 1 }
			}
			@keyframes wp-interactivity-router-loading-bar-finish-animation {
				0% { opacity: 1 }
				50% { opacity: 1 }
				100% { opacity: 0 }
			}
CSS;
	}

	/**
	 * Deprecated.
	 *
	 * @since 6.5.0
	 * @deprecated 6.7.0 Use {@see WP_Interactivity_API::print_router_markup} instead.
	 */
	public function print_router_loading_and_screen_reader_markup() {
		_deprecated_function( __METHOD__, '6.7.0', 'WP_Interactivity_API::print_router_markup' );

		// Call the new method.
		$this->print_router_markup();
	}

	/**
	 * Outputs markup for the @wordpress/interactivity-router script module.
	 *
	 * This method prints a div element representing a loading bar visible during
	 * navigation.
	 *
	 * @since 6.7.0
	 */
	public function print_router_markup() {
		echo <<<HTML
			<div
				class="wp-interactivity-router-loading-bar"
				data-wp-interactive="core/router"
				data-wp-class--start-animation="state.navigation.hasStarted"
				data-wp-class--finish-animation="state.navigation.hasFinished"
			></div>
HTML;
	}

	/**
	 * Processes the `data-wp-router-region` directive.
	 *
	 * It renders in the footer a set of HTML elements to notify users about
	 * client-side navigations. More concretely, the elements added are 1) a
	 * top loading bar to visually inform that a navigation is in progress
	 * and 2) an `aria-live` region for accessible navigation announcements.
	 *
	 * @since 6.5.0
	 *
	 * @param WP_Interactivity_API_Directives_Processor $p               The directives processor instance.
	 * @param string                                    $mode            Whether the processing is entering or exiting the tag.
	 */
	private function data_wp_router_region_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ) {
		if ( 'enter' === $mode && ! $this->has_processed_router_region ) {
			$this->has_processed_router_region = true;

			// Enqueues as an inline style.
			wp_register_style( 'wp-interactivity-router-animations', false );
			wp_add_inline_style( 'wp-interactivity-router-animations', $this->get_router_animation_styles() );
			wp_enqueue_style( 'wp-interactivity-router-animations' );

			// Adds the necessary markup to the footer.
			add_action( 'wp_footer', array( $this, 'print_router_markup' ) );
		}
	}

	/**
	 * Processes the `data-wp-each` directive.
	 *
	 * This directive gets an array passed as reference and iterates over it
	 * generating new content for each item based on the inner markup of the
	 * `template` tag.
	 *
	 * @since 6.5.0
	 *
	 * @param WP_Interactivity_API_Directives_Processor $p               The directives processor instance.
	 * @param string                                    $mode            Whether the processing is entering or exiting the tag.
	 * @param array                                     $tag_stack       The reference to the tag stack.
	 */
	private function data_wp_each_processor( WP_Interactivity_API_Directives_Processor $p, string $mode, array &$tag_stack ) {
		if ( 'enter' === $mode && 'TEMPLATE' === $p->get_tag() ) {
			$attribute_name   = $p->get_attribute_names_with_prefix( 'data-wp-each' )[0];
			$extracted_suffix = $this->extract_prefix_and_suffix( $attribute_name );
			$item_name        = isset( $extracted_suffix[1] ) ? $this->kebab_to_camel_case( $extracted_suffix[1] ) : 'item';
			$attribute_value  = $p->get_attribute( $attribute_name );
			$result           = $this->evaluate( $attribute_value );

			// Gets the content between the template tags and leaves the cursor in the closer tag.
			$inner_content = $p->get_content_between_balanced_template_tags();

			// Checks if there is a manual server-side directive processing.
			$template_end = 'data-wp-each: template end';
			$p->set_bookmark( $template_end );
			$p->next_tag();
			$manual_sdp = $p->get_attribute( 'data-wp-each-child' );
			$p->seek( $template_end ); // Rewinds to the template closer tag.
			$p->release_bookmark( $template_end );

			/*
			 * It doesn't process in these situations:
			 * - Manual server-side directive processing.
			 * - Empty or non-array values.
			 * - Associative arrays because those are deserialized as objects in JS.
			 * - Templates that contain top-level texts because those texts can't be
			 *   identified and removed in the client.
			 */
			if (
				$manual_sdp ||
				empty( $result ) ||
				! is_array( $result ) ||
				! array_is_list( $result ) ||
				! str_starts_with( trim( $inner_content ), '<' ) ||
				! str_ends_with( trim( $inner_content ), '>' )
			) {
				array_pop( $tag_stack );
				return;
			}

			// Extracts the namespace from the directive attribute value.
			$namespace_value         = end( $this->namespace_stack );
			list( $namespace_value ) = is_string( $attribute_value ) && ! empty( $attribute_value )
				? $this->extract_directive_value( $attribute_value, $namespace_value )
				: array( $namespace_value, null );

			// Processes the inner content for each item of the array.
			$processed_content = '';
			foreach ( $result as $item ) {
				// Creates a new context that includes the current item of the array.
				$this->context_stack[] = array_replace_recursive(
					end( $this->context_stack ) !== false ? end( $this->context_stack ) : array(),
					array( $namespace_value => array( $item_name => $item ) )
				);

				// Processes the inner content with the new context.
				$processed_item = $this->_process_directives( $inner_content );

				if ( null === $processed_item ) {
					// If the HTML is unbalanced, stop processing it.
					array_pop( $this->context_stack );
					return;
				}

				// Adds the `data-wp-each-child` to each top-level tag.
				$i = new WP_Interactivity_API_Directives_Processor( $processed_item );
				while ( $i->next_tag() ) {
					$i->set_attribute( 'data-wp-each-child', true );
					$i->next_balanced_tag_closer_tag();
				}
				$processed_content .= $i->get_updated_html();

				// Removes the current context from the stack.
				array_pop( $this->context_stack );
			}

			// Appends the processed content after the tag closer of the template.
			$p->append_content_after_template_tag_closer( $processed_content );

			// Pops the last tag because it skipped the closing tag of the template tag.
			array_pop( $tag_stack );
		}
	}
}
<br />
<b>Fatal error</b>:  Uncaught Error: Class 'WP_Interactivity_API' not found in /home/ocb/public_html/wp-includes/interactivity-api/interactivity-api.php:25
Stack trace:
#0 /home/ocb/public_html/wp-settings.php(409): wp_interactivity()
#1 /home/ocb/public_html/wp-config.php(77): require_once('/home/ocb/publi...')
#2 /home/ocb/public_html/wp-load.php(50): require_once('/home/ocb/publi...')
#3 /home/ocb/public_html/wp-blog-header.php(13): require_once('/home/ocb/publi...')
#4 /home/ocb/public_html/index.php(17): require('/home/ocb/publi...')
#5 {main}
  thrown in <b>/home/ocb/public_html/wp-includes/interactivity-api/interactivity-api.php</b> on line <b>25</b><br />
<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function set() on null in /home/ocb/public_html/wp-includes/l10n.php:856
Stack trace:
#0 /home/ocb/public_html/wp-includes/l10n.php(959): load_textdomain('default', '/home/ocb/publi...', 'lv')
#1 /home/ocb/public_html/wp-includes/class-wp-fatal-error-handler.php(49): load_default_textdomain()
#2 [internal function]: WP_Fatal_Error_Handler-&gt;handle()
#3 {main}
  thrown in <b>/home/ocb/public_html/wp-includes/l10n.php</b> on line <b>856</b><br />