在下php新手，在看wordpress代码时，对header文件始终不解（位置:wp-content/temes/twentyeleven/header.php）。
特来请教各位：
该文件代码中并include操作，其中如bloginfo(),wp_head()等外部函数如何可以调用？
此种开发模式如何实现？望各位能为在下讲解下，或提供资料，在下不甚感激。
- PHP code
<?php/** * The Header for our theme. * * Displays all of the <head> section and everything up till <div id="main"> * * @package WordPress * @subpackage Twenty_Eleven * @since Twenty Eleven 1.0 */?><!DOCTYPE html><!--[if IE 6]><html id="ie6" <?php language_attributes(); ?>><![endif]--><!--[if IE 7]><html id="ie7" <?php language_attributes(); ?>><![endif]--><!--[if IE 8]><html id="ie8" <?php language_attributes(); ?>><![endif]--><!--[if !(IE 6) | !(IE 7) | !(IE 8) ]><!--><html <?php language_attributes(); ?>><!--<![endif]--><head><meta charset="<?php bloginfo( 'charset' ); ?>" /><meta name="viewport" content="width=device-width" /><title><?php /* * Print the <title> tag based on what is being viewed. */ global $page, $paged; wp_title( '|', true, 'right' ); // Add the blog name. bloginfo( 'name' ); // Add the blog description for the home/front page. $site_description = get_bloginfo( 'description', 'display' ); if ( $site_description && ( is_home() || is_front_page() ) ) echo " | $site_description"; // Add a page number if necessary: if ( $paged >= 2 || $page >= 2 ) echo ' | ' . sprintf( __( 'Page %s', 'twentyeleven' ), max( $paged, $page ) ); ?></title><link rel="profile" href="http://gmpg.org/xfn/11" /><link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo( 'stylesheet_url' ); ?>" /><link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>" /><!--[if lt IE 9]><script src="<?php echo get_template_directory_uri(); ?>/js/html5.js" type="text/javascript"></script><![endif]--><?php /* We add some JavaScript to pages with the comment form * to support sites with threaded comments (when in use). */ if ( is_singular() && get_option( 'thread_comments' ) ) wp_enqueue_script( 'comment-reply' ); /* Always have wp_head() just before the closing </head> * tag of your theme, or you will break many plugins, which * generally use this hook to add elements to <head> such * as styles, scripts, and meta tags. */ wp_head();?></head><body <?php body_class(); ?>><div id="page" class="hfeed"> <header id="branding" role="banner"> <hgroup> <h1 id="site-title"><span><a href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></span></h1> <h2 id="site-description"><?php bloginfo( 'description' ); ?></h2> </hgroup> <?php // Check to see if the header image has been removed $header_image = get_header_image(); if ( $header_image ) : // Compatibility with versions of WordPress prior to 3.4. if ( function_exists( 'get_custom_header' ) ) { // We need to figure out what the minimum width should be for our featured image. // This result would be the suggested width if the theme were to implement flexible widths. $header_image_width = get_theme_support( 'custom-header', 'width' ); } else { $header_image_width = HEADER_IMAGE_WIDTH; } ?> <a href="<?php echo esc_url( home_url( '/' ) ); ?>"> <?php // The header image // Check if this is a post or page, if it has a thumbnail, and if it's a big one if ( is_singular() && has_post_thumbnail( $post->ID ) && ( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), array( $header_image_width, $header_image_width ) ) ) && $image[1] >= $header_image_width ) : // Houston, we have a new header image! echo get_the_post_thumbnail( $post->ID, 'post-thumbnail' ); else : // Compatibility with versions of WordPress prior to 3.4. if ( function_exists( 'get_custom_header' ) ) { $header_image_width = get_custom_header()->width; $header_image_height = get_custom_header()->height; } else { $header_image_width = HEADER_IMAGE_WIDTH; $header_image_height = HEADER_IMAGE_HEIGHT; } ?> <img src="<?php header_image(); ?>" width="<?php echo $header_image_width; ?>" height="<?php echo $header_image_height; ?>" alt="" /> <?php endif; // end check for featured image or standard header ?> </a> <?php endif; // end check for removed header image ?> <?php // Has the text been hidden? if ( 'blank' == get_header_textcolor() ) : ?> <div class="only-search<?php if ( $header_image ) : ?> with-image<?php endif; ?>"> <?php get_search_form(); ?> </div> <?php else : ?> <?php get_search_form(); ?> <?php endif; ?> <nav id="access" role="navigation"> <h3 class="assistive-text"><?php _e( 'Main menu', 'twentyeleven' ); ?></h3> <?php /* Allow screen readers / text browsers to skip the navigation menu and get right to the good stuff. */ ?> <div class="skip-link"><a class="assistive-text" href="#content" title="<?php esc_attr_e( 'Skip to primary content', 'twentyeleven' ); ?>"><?php _e( 'Skip to primary content', 'twentyeleven' ); ?></a></div> <div class="skip-link"><a class="assistive-text" href="#secondary" title="<?php esc_attr_e( 'Skip to secondary content', 'twentyeleven' ); ?>"><?php _e( 'Skip to secondary content', 'twentyeleven' ); ?></a></div> <?php /* Our navigation menu. If one isn't filled out, wp_nav_menu falls back to wp_page_menu. The menu assigned to the primary location is the one used. If one isn't assigned, the menu with the lowest ID is used. */ ?> <?php wp_nav_menu( array( 'theme_location' => 'primary' ) ); ?> </nav><!-- #access --> </header><!-- #branding --> <div id="main">