Form_Settings_Page::register()

	public function register() {
		$this->add_page_content();

		foreach ( $this->tabs as $id => $tab_args ) {
			foreach ( $tab_args['field_manager']->get_fields() as $field ) {
				if ( ! isset( $this->sections[ $field->section ] ) ) {
					continue;
				}

				if ( ! isset( $this->subtabs[ $this->sections[ $field->section ]['subtab'] ] ) ) {
					continue;
				}

				$tab_subtab_slug = $this->subtabs[ $this->sections[ $field->section ]['subtab'] ]['tab'] . '_' . $this->sections[ $field->section ]['subtab'];

				add_settings_field( $field->id, $field->label, array( $this, 'render_field' ), $tab_subtab_slug, $field->section, array(
					'label_for'      => $tab_args['field_manager']->make_id( $field->id ),
					'field_instance' => $field,
				) );
			}

			register_setting( $id, $id );
			add_filter( "sanitize_option_{$id}", array( $this, 'validate' ), 10, 2 );
		}

		foreach ( $this->sections as $id => $section_args ) {
			if ( ! isset( $this->subtabs[ $section_args['subtab'] ] ) ) {
				continue;
			}

			$tab_subtab_slug = $this->subtabs[ $section_args['subtab'] ]['tab'] . '_' . $section_args['subtab'];

			add_settings_section( $id, $section_args['title'], array( $this, 'render_section_description' ), $tab_subtab_slug );
		}
	}