is_favicon example

    if ( is_preview() && get_query_var( 'p' ) && 'publish' === get_post_status( get_query_var( 'p' ) ) ) {
        if ( ! isset( $_GET['preview_id'] )
            || ! isset( $_GET['preview_nonce'] )
            || ! wp_verify_nonce( $_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'] )
        ) {
            $wp_query->is_preview = false;
        }
    }

    if ( is_admin() || is_search() || is_preview() || is_trackback() || is_favicon()
        || ( $is_IIS && ! iis7_supports_permalinks() )
    ) {
        return;
    }

    if ( ! $requested_url && isset( $_SERVER['HTTP_HOST'] ) ) {
        // Build the URL in the address bar.         $requested_url  = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }

    

// Process feeds and trackbacks even if not using themes. if ( is_robots() ) {
    /** * Fired when the template loader determines a robots.txt request. * * @since 2.1.0 */
    do_action( 'do_robots' );
    return;
} elseif ( is_favicon() ) {
    /** * Fired when the template loader determines a favicon.ico request. * * @since 5.4.0 */
    do_action( 'do_favicon' );
    return;
} elseif ( is_feed() ) {
    do_feed();
    return;
} elseif ( is_trackback() ) {
    

function is_favicon() {
    global $wp_query;

    if ( ! isset( $wp_query ) ) {
        _doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
        return false;
    }

    return $wp_query->is_favicon();
}

/** * Determines whether the query is for a search. * * For more information on this and similar theme functions, check out * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/ * Conditional Tags} article in the Theme Developer Handbook. * * @since 1.5.0 * * @global WP_Query $wp_query WordPress Query object. * * @return bool Whether the query is for a search. */

return;
        }

        // If we've already issued a 404, bail.         if ( is_404() ) {
            return;
        }

        $set_404 = true;

        // Never 404 for the admin, robots, or favicon.         if ( is_admin() || is_robots() || is_favicon() ) {
            $set_404 = false;

            // If posts were found, check for paged content.         } elseif ( $wp_query->posts ) {
            $content_found = true;

            if ( is_singular() ) {
                $post = isset( $wp_query->post ) ? $wp_query->post : null;
                $next = '<!--nextpage-->';

                // Check for paged content that exceeds the max number of pages.