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">