Issue #1269594: explain better what system pages are.

print.admin.inc

@@ -268,6 +268,7 @@ function print_html_settings() {
   $form['settings']['adv_link']['print_html_sys_link_visibility'] = array(
     '#type' => 'radios',
     '#title' => t('Show link in system (non-content) pages'),
+    '#description' => 'Any page that is not a Drupal node. Usually pages generated by Drupal or a module such as Views or Panels.',
     '#default_value' => variable_get('print_html_sys_link_visibility', PRINT_HTML_SYS_LINK_VISIBILITY_DEFAULT),
     '#options' => array(t('Show on every page except the listed pages.'), t('Show on only the listed pages.')),
   );

print_mail/print_mail.admin.inc

@@ -100,6 +100,7 @@ function print_mail_settings() {
   $form['settings']['adv_link']['print_mail_sys_link_visibility'] = array(
     '#type' => 'radios',
     '#title' => t('Show link in system (non-content) pages'),
+    '#description' => 'Any page that is not a Drupal node. Usually pages generated by Drupal or a module such as Views or Panels.',
     '#default_value' => variable_get('print_mail_sys_link_visibility', PRINT_MAIL_SYS_LINK_VISIBILITY_DEFAULT),
     '#options' => array(t('Show on every page except the listed pages.'), t('Show on only the listed pages.')),
   );

print_pdf/print_pdf.admin.inc

@@ -109,6 +109,7 @@ function print_pdf_settings() {
     $form['settings']['adv_link']['print_pdf_sys_link_visibility'] = array(
       '#type' => 'radios',
       '#title' => t('Show link in system (non-content) pages'),
+      '#description' => 'Any page that is not a Drupal node. Usually pages generated by Drupal or a module such as Views or Panels.',
       '#default_value' => variable_get('print_pdf_sys_link_visibility', PRINT_PDF_SYS_LINK_VISIBILITY_DEFAULT),
       '#options' => array(t('Show on every page except the listed pages.'), t('Show on only the listed pages.')),
     );