<?php
/* Use the admin_menu action to define the custom boxes */
add_action('admin_menu', 'myplugin_add_custom_box');

/* Use the save_post action to do something with the data entered */
add_action('save_post', 'myplugin_save_postdata');

/* Adds a custom section to the "advanced" Post and Page edit screens */
function myplugin_add_custom_box() {

if( function_exists( 'add_meta_box' )) {
add_meta_box( 'myplugin_sectionid', __( 'My Post Section Title', 'myplugin_textdomain' ),
'myplugin_inner_custom_box', 'post', 'advanced' );
add_meta_box( 'myplugin_sectionid', __( 'My Post Section Title', 'myplugin_textdomain' ),
'myplugin_inner_custom_box', 'page', 'advanced' );
} else {
add_action('dbx_post_advanced', 'myplugin_old_custom_box' );
add_action('dbx_page_advanced', 'myplugin_old_custom_box' );
}
}

/* Prints the inner fields for the custom post/page section */
function myplugin_inner_custom_box() {

// Use nonce for verification

echo '<input type="hidden" name="myplugin_noncename" id="myplugin_noncename" value="' .
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';

// The actual fields for data entry

echo '<label for="myplugin_new_field">' . __("Description for this field", 'myplugin_textdomain' ) . '</label> ';
echo '<input type="text" name="myplugin_new_field" value="whatever" size="25" />';
}

/* Prints the edit form for pre-WordPress 2.5 post/page */
function myplugin_old_custom_box() {

echo '<div class="dbx-b-ox-wrapper">' . "\n";
echo '<fieldset id="myplugin_fieldsetid" class="dbx-box">' . "\n";
echo '<div class="dbx-h-andle-wrapper"><h3 class="dbx-handle">' .
__( 'My Post Section Title', 'myplugin_textdomain' ) . "</h3></div>";

echo '<div class="dbx-c-ontent-wrapper"><div class="dbx-content">';

// output editing form

myplugin_inner_custom_box();

// end wrapper

echo "</div></div></fieldset></div>\n";
}

/* When the post is saved, saves our custom data */
function myplugin_save_postdata( $post_id ) {

// verify this came from the our screen and with proper authorization,
// because save_post can be triggered at other times

if ( !wp_verify_nonce( $_POST['myplugin_noncename'], plugin_basename(__FILE__) )) {
return $post_id;
}

// verify if this is an auto save routine. If it is our form has not been submitted, so we dont want
// to do anything
if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE )
return $post_id;


// Check permissions
if ( 'page' == $_POST['post_type'] ) {
if ( !current_user_can( 'edit_page', $post_id ) )
return $post_id;
} else {
if ( !current_user_can( 'edit_post', $post_id ) )
return $post_id;
}

// OK, we're authenticated: we need to find and save the data

$mydata = $_POST['myplugin_new_field'];

// Do something with $mydata
// probably using add_post_meta(), update_post_meta(), or
// a custom table (see Further Reading section below)

return $mydata;
}
?>