Not a 4.7 module

The print module is flagged as a 4.7.x module, but still uses the 'old' form API.

The print_settings function hereunder works in 4.7 without complaining:

function print_settings() {
  $form['print_css'] = array(
  	'#type' => 'textfield',
  	'#title' => t('Stylesheet URL'),
  	'#default_value' => variable_get('print_css', 'misc/print.css'),
  	'#size' => 60,
  	'#maxlength' => 64,
  	'#description' => t('The URL to your print cascading stylesheet.'),
  );

  $form['print_urls'] = array(
    '#type' => 'checkbox',
    '#title' => t('Printer friendly URLs'),
    '#return_value' => 1,
    '#default_value' => variable_get('print_urls', 0),
  );
  
  $form['elements'] = array(
    '#type' => 'fieldset',
    '#title' => t('Print page elements'),
  );
  
  $form['elements']['print_show_link'] = array(
    '#type' => 'radios',
    '#title' => t('Printer friendly page link'),
    '#default_value' => variable_get('print_show_link', 1),
    '#options' => array(t("Disabled"), t("Enabled")),
    '#description' => t("Enable or disable the 'printer friendly page' link for each node. Even if the link is disabled, you can still view the print version of a node by going to 'node/nid/print' where nid is the numeric id of the node."),
  );

  return $form;
}