<?php
/**
 * Allow or deny a given operation on a node.
 *
 * When a node is accessed, a module implementing node access will be asked
 * for its opinion whether the operation should be allowed on the node.
 * The module must respond with either TRUE to allow the operation, FALSE
 * to deny it, or NULL if it is undecided.
 *
 * @param $op
 *   The node operation to be performed, such as "view", "update" or "delete".
 * @param $node
 *   The node object on which the operation is to be performed.
 * @param $published
 *   Indicates whether the node is published. Operations on unpublished nodes
 *   should generally not be allowed.
 * @param $account
 *   The user object performing the operation.
 *
 * @ingroup node_access
 */
function hook_node_access($op, $node, $published, $account) {
  // Allow viewing of all pages and deny deletion of pages.
  if ($node->type == 'page' && $published) {
    if ($op == 'view') {
      return TRUE;
    } elseif ($op == 'edit') {
      return NULL;
    } elseif ($op == 'delete') {
      return FALSE;
    }
  }
  return NULL;
}
?>