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<?php/** * Implementation of hook_form_alter(). */function pubrev_form_alter(&$form, $form_state, $form_id) {  if ($form['#id'] == 'node_form') {    $form['options']['pubrev_allow'] = array(      '#type' => 'checkbox',      '#title' => t('Public revision access'),      '#default_value' => variable_get('pubrev_allow', false),      '#description' => t('Allow anonymous users to view the revisions of this page.'),    );  }}