g $type The type of generator to return - (html|xhtml|atom|rss2|rdf|comment|export).
 * @return string|void The HTML content for the generator.
 */
function get_the_generator( $type = '' ) {
	if ( empty( $type ) ) {

		$current_filter = current_filter();
		if ( empty( $current_filter ) ) {
			return;
		}

		switch ( $current_filter ) {
			case 'rss2_head':
			case 'commentsrss2_head':
				$type = 'rss2';
				break;
			case 'rss_head':
			case 'opml_head':
				$type = 'comment';
				break;
			case 'rdf_header':
				$type = 'rdf';
				break;
			case 'atom_head':
			case 'comments_atom_head':
			case 'app_head':
				$type = 'atom';
				break;
		}
	}

	switch ( $type ) {
		case 'html':
			$gen = '<meta name="generator" content="WordPress ' . esc_attr( get_bloginfo( 'version' ) ) . '">';
			break;
		case 'xhtml':
			$gen = '<meta name="generator" content="WordPress ' . esc_attr( get_bloginfo( 'version' ) ) . '" />';
			break;
		case 'atom':
			$gen = '<generator uri="https://wordpress.org/" version="' . esc_attr( get_bloginfo_rss( 'version' ) ) . '">WordPress</generator>';
			break;
		case 'rss2':
			$gen = '<generator>' . sanitize_url( 'https://wordpress.org/?v=' . get_bloginfo_rss( 'version' ) ) . '</generator>';
			break;
		case 'rdf':
			$gen = '<admin:generatorAgent rdf:resource="' . sanitize_url( 'https://wordpress.org/?v=' . get_bloginfo_rss( 'version' ) ) . '" />';
			break;
		case 'comment':
			$gen = '<!-- generator="WordPress/' . esc_attr( get_bloginfo( 'version' ) ) . '" -->';
			break;
		case 'export':
			$gen = '<!-- generator="WordPress/' . esc_attr( get_bloginfo_rss( 'version' ) ) . '" created="' . gmdate( 'Y-m-d H:i' ) . '" -->';
			break;
	}

	/**
	 * Filters the HTML for the retrieved generator type.
	 *
	 * The dynamic portion of the hook name, `$type`, refers to the generator type.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_the_generator_atom`
	 *  - `get_the_generator_comment`
	 *  - `get_the_generator_export`
	 *  - `get_the_generator_html`
	 *  - `get_the_generator_rdf`
	 *  - `get_the_generator_rss2`
	 *  - `get_the_generator_xhtml`
	 *
	 * @since 2.5.0
	 *
	 * @param string $gen  The HTML markup output to wp_head().
	 * @param string $type The type of generator. Accepts 'html', 'xhtml', 'atom',
	 *                     'rss2', 'rdf', 'comment', 'export'.
	 */
	return apply_filters( "get_the_generator_{$type}", $gen, $type );
}

/**
 * Outputs the HTML checked attribute.
 *
 * Compares the first two arguments and if identical marks as checked.
 *
 * @since 1.0.0
 *
 * @param mixed $checked One of the values to compare.
 * @param mixed $current Optional. The other value to compare if not just true.
 *                       Default true.
 * @param bool  $display Optional. Whether to echo or just return the string.
 *                       Default true.
 * @return string HTML attribute or empty string.
 */
function checked( $checked, $current = true, $display = true ) {
	return __checked_selected_helper( $checked, $current, $display, 'checked' );
}

/**
 * Outputs the HTML selected attribute.
 *
 * Compares the first two arguments and if identical marks as selected.
 *
 * @since 1.0.0
 *
 * @param mixed $selected One of the values to compare.
 * @param mixed $current  Optional. The other value to compare if not just true.
 *                        Default true.
 * @param bool  $display  Optional. Whether to echo or just return the string.
 *                        Default true.
 * @return string HTML attribute or empty string.
 */
function selected( $selected, $current = true, $display = true ) {
	return __checked_selected_helper( $selected, $current, $display, 'selected' );
}

/**
 * Outputs the HTML disabled attribute.
 *
 * Compares the first two arguments and if identical marks as disabled.
 *
 * @since 3.0.0
 *
 * @param mixed $disabled One of the values to compare.
 * @param mixed $current  Optional. The other value to compare if not just true.
 *                        Default true.
 * @param bool  $display  Optional. Whether to echo or just return the string.
 *                        Default true.
 * @return string HTML attribute or empty string.
 */
function disabled( $disabled, $current = true, $display = true ) {
	return __checked_selected_helper( $disabled, $current, $display, 'disabled' );
}

/**
 * Outputs the HTML readonly attribute.
 *
 * Compares the first two arguments and if identical marks as readonly.
 *
 * @since 5.9.0
 *
 * @param mixed $readonly_value One of the values to compare.
 * @param mixed $current        Optional. The other value to compare if not just true.
 *                              Default true.
 * @param bool  $display        Optional. Whether to echo or just return the string.
 *                              Default true.
 * @return string HTML attribute or empty string.
 */
function wp_readonly( $readonly_value, $current = true, $display = true ) {
	return __checked_selected_helper( $readonly_value, $current, $display, 'readonly' );
}

/*
 * Include a compat `readonly()` function on PHP < 8.1. Since PHP 8.1,
 * `readonly` is a reserved keyword and cannot be used as a function name.
 * In order to avoid PHP parser errors, this function was extracted
 * to a separate file and is only included conditionally on PHP < 8.1.
 */
if ( PHP_VERSION_ID < 80100 ) {
	require_once __DIR__ . '/php-compat/readonly.php';
}

/**
 * Private helper function for checked, selected, disabled and readonly.
 *
 * Compares the first two arguments and if identical marks as `$type`.
 *
 * @since 2.8.0
 * @access private
 *
 * @param mixed  $helper  One of the values to compare.
 * @param mixed  $current The other value to compare if not just true.
 * @param bool   $display Whether to echo or just return the string.
 * @param string $type    The type of checked|selected|disabled|readonly we are doing.
 * @return string HTML attribute or empty string.
 */
function __checked_selected_helper( $helper, $current, $display, $type ) { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionDoubleUnderscore,PHPCompatibility.FunctionNameRestrictions.ReservedFunctionNames.FunctionDoubleUnderscore
	if ( (string) $helper === (string) $current ) {
		$result = " $type='$type'";
	} else {
		$result = '';
	}

	if ( $display ) {
		echo $result;
	}

	return $result;
}

/**
 * Assigns a visual indicator for required form fields.
 *
 * @since 6.1.0
 *
 * @return string Indicator glyph wrapped in a `span` tag.
 */
function wp_required_field_indicator() {
	/* translators: Character to identify required form fields. */
	$glyph     = __( '*' );
	$indicator = '<span class="required">' . esc_html( $glyph ) . '</span>';

	/**
	 * Filters the markup for a visual indicator of required form fields.
	 *
	 * @since 6.1.0
	 *
	 * @param string $indicator Markup for the indicator element.
	 */
	return apply_filters( 'wp_required_field_indicator', $indicator );
}

/**
 * Creates a message to explain required form fields.
 *
 * @since 6.1.0
 *
 * @return string Message text and glyph wrapped in a `span` tag.
 */
function wp_required_field_message() {
	$message = sprintf(
		'<span class="required-field-message">%s</span>',
		/* translators: %s: Asterisk symbol (*). */
		sprintf( __( 'Required fields are marked %s' ), wp_required_field_indicator() )
	);

	/**
	 * Filters the message to explain required form fields.
	 *
	 * @since 6.1.0
	 *
	 * @param string $message Message text and glyph wrapped in a `span` tag.
	 */
	return apply_filters( 'wp_required_field_message', $message );
}

/**
 * Default settings for heartbeat.
 *
 * Outputs the nonce used in the heartbeat XHR.
 *
 * @since 3.6.0
 *
 * @param array $settings
 * @return array Heartbeat settings.
 */
function wp_heartbeat_settings( $settings ) {
	if ( ! is_admin() ) {
		$settings['ajaxurl'] = admin_url( 'admin-ajax.php', 'relative' );
	}

	if ( is_user_logged_in() ) {
		$settings['nonce'] = wp_create_nonce( 'heartbeat-nonce' );
	}

	return $settings;
}