How to produce a simple Wordpress function in functions.php

I wish to create a function something similar to custom_header() and also the code within the function is

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" <?php language_attributes(); ?>>
<head profile="http://gmpg.org/xfn/11">
<meta http-equiv="Content-Type" content="text/html; charset=<?php bloginfo( 'charset' ); ?>" />
<title><?php bloginfo( 'name' ); ?></title>
<link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo( 'stylesheet_url' ); ?>" />
<link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>" />
<?php if ( is_singular() && get_option( 'thread_comments' ) ) wp_enqueue_script( 'comment-reply' ); ?>

<?php wp_head(); ?>
</head>

<body <?php body_class(); ?>>

So during my header.php I simply write <?php custom_header(); ?> rather than HTML codes above.

Tell me

Quite simple:

function custom_header(){
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" <?php language_attributes(); ?>>
<head profile="http://gmpg.org/xfn/11">
<meta http-equiv="Content-Type" content="text/html; charset=<?php bloginfo( 'charset' ); ?>" />
<title><?php bloginfo( 'name' ); ?></title>
<link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo( 'stylesheet_url' ); ?>" />
<link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>" />
<?php if ( is_singular() && get_option( 'thread_comments' ) ) wp_enqueue_script( 'comment-reply' ); ?>

<?php wp_head(); ?>
</head>

<body <?php body_class(); ?>>
<?php
}