Add child theme settings to Thematic theme options page

childtheme_separate_options.php

<?php

add_action ('admin_init', 'childtheme_opt_init');
/**
 * Add childtheme settings to the thematic theme 
 * 
 * This will create a separate setting in the database, but
 * add the settings to the existing theme options page in Thematic
 **/
function childtheme_opt_init() {
	
	/* Register childtheme setting separate from thematic */
	register_setting(
		'thematic_opt_group',       			// Add to thematic settings page group
		'childtheme_options',				// Name of the database option
		'childtheme_options_validate' 			// The sanitization callback for the options
	);

	/* Add a settings section for our childtheme */
	add_settings_section( 
		'childtheme_section',				// Slug of this section
		__( 'Childtheme title', 'child-textdomain' ), 	// Title of this section (optional, can be empty string)
		'childtheme_section_html', 			// Callback function for this section description
		'thematic_theme_opt' 				// Add to the thematic setting sections
	);

	/* Add settings fields to the settings section */
	add_settings_field( 
		'childtheme_textarea', 				// Slug of the option
		__( 'Write some text', 'child-textdomain' ), 	// Title of the option
		'childtheme_textarea_html', 			// Callback for rendering the option
		'thematic_theme_opt', 				// Add to the thematic setting sections
		'childtheme_section' 				// Add to the section defined above
	);

}


/**
 * Return default childtheme options.
 * 
 * @return array $childtheme_default_opt The default options
 */
function childtheme_default_opt() {
	
	$childtheme_default_opt = array(
		'childtheme_textarea' 	=> 'Bacon!'
	);

	return $childtheme_default_opt;
}


/**
 * Validate our child theme options
 * 
 * Thematic takes care of the thematic form data, we only need 
 * to worry about the childtheme settings we have created
 * 
 * @param   array  $input   Raw input from the form
 * @return  array  $output  Sanitized and cleaned data ready for database
 **/
function childtheme_options_validate( $input ) {
	
	/* Pull existing settings from database */
	$output = get_option( 'childtheme_options', childtheme_default_opt() );	
	
	/* Allow basic HTML and WP shortcodes */
	if ( isset( $input['childtheme_textarea'] ) ) {
		$output['childtheme_textarea'] = wp_kses_post( $input['childtheme_textarea'] ) ;	
	}
	
	return $output;
}



/**
 * Render the description of settings section: childtheme_section
 **/
function childtheme_section_html() {
	// sound of one hand clapping
}


/**
 * Render the textarea for childtheme setting: childtheme_textarea
 */
function childtheme_textarea_html() { 
	$options = thematic_get_wp_opt( 'childtheme_options', childtheme_default_opt() );
?>
	<textarea rows="5" cols="94" id="childtheme_textarea" name="childtheme_options[childtheme_textarea]"><?php echo $options['childtheme_textarea']; ?></textarea>
<?php
}