我很难在我创建的主题页面上显示我的“Hello World”。这一切至少看起来是正确的（但显然不是）-我在这里遗漏了什么？

// Add Theme Options to menu

function add_theme_menu_item() {

add_theme_page("Theme Panel", "Theme Panel", "manage_options", "theme-panel", "initialize_theme_options", null, 99);

}

add_action("admin_menu", "add_theme_menu_item");

 /**
 * Initializes the theme options page by registering the Sections,
  * Fields, and Settings.
 *
 * This function is registered with the \'admin_init\' hook.
 */

 function initialize_theme_options() {

// First, we register a section. This is necessary since all future options must belong to one.

add_settings_section(

    // ID used to identify this section and with which to register options
    \'main_settings_section\',

    // Title to be displayed on the administration page
    \'Main Theme Options\',

    // Callback used to render the description of the section

    \'main_settings_callback\', 

    // Page

    \'theme-panel\'

);

} 

add_action(\'admin_init\', \'initialize_theme_options\');

 // end initialize_theme_options

/* ------------------------------------------------------------------------ *
* Section Callbacks
* ------------------------------------------------------------------------ */

/**
* This function provides a simple description for the General Options page. 
*
* It is called from the \'initialize_theme_options\' function by being passed as a parameter
* in the add_settings_section function.
*/

function main_settings_callback() {

  echo \'Hello world.\';

} 
// end main_settings_callback