public function form( $instance ) {
		$title = ( isset( $instance['title'] ) ? $instance['title'] : '' );
		?>
		<p><label for="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>"><?php esc_html_e( 'Title:', 'inventory-presser' ); ?></label>
		<input class="widefat" id="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>" name="<?php echo esc_attr( $this->get_field_name( 'title' ) ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" /></p>
		<?php
		$args                   = array(
			'public' => true,
		);
		$already_turned_on_keys = array();
		if ( isset( $instance['post-meta-keys'] ) ) {
			$already_turned_on_keys = explode( '|', $instance['post-meta-keys'] );
		}

		echo '<p>' . esc_html__( 'Which fields should users be allowed to use as sort fields?', 'inventory-presser' )
			. '</p><dl>';

		foreach ( $this->get_post_meta_keys_and_labels( $instance ) as $key => $label ) {
			// output checkbox for each one.
			echo '<dt>';
			$title = 'Allow users to order by ' . $key; // title attribute for checkbox and label.
			echo '<input type="checkbox" id="' . esc_attr( $this->get_field_id( 'obpm-key-' . $key ) )
			. '" name="obpm-key-' . esc_attr( $key ) . '"'
			. checked( in_array( $key, $already_turned_on_keys, true ), true, false )
			. ' title="' . esc_attr( $title ) . '"/>'
			. '<label for="' . esc_attr( $this->get_field_id( 'obpm-key-' . $key ) )
			. '" title="' . esc_attr( $title ) . '">'
			. esc_html( $this->prettify_meta_key( $key ) ) . '</label>'
			. '</dt>' // and a text box for a label.
			. '<dd>'
			. '<label for="' . esc_attr( $this->get_field_id( 'obpm-label-' . $key ) )
			. '">Label</label> '
			. '<input type="text" id="' . esc_attr( $this->get_field_id( 'obpm-label-' . $key ) ) . '"'
			. ' name="obpm-label-' . esc_attr( $key ) . '" '
			. 'value="' . esc_attr( $label ) . '" title="Label for '
			. esc_attr( $key ) . '" /></dd>';
		}
		echo '</dl>';
	}