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if page is parent or child

If Page Is Parent or Child Last updated on: SEPTEMBER 11, 2009  There are built in conditional WordPress functions for testing for a page:  if ( is_page(2) ) {   // stuff } Or for testing if a page is a child of a certain page:  if ( $post->post_parent == '2' ) {   // stuff } But there is no built in function that combines these two things, which is a fairly common need. For example, loading a special CSS page for a whole "branch" of content. Like a "videos" page and all its children individual videos pages.  This function (add to functions.php file) creates new logical function to be used in this way:  function is_tree($pid) {      // $pid = The ID of the page we're looking for pages underneath  global $post;         // load details about this page  if(is_page()&&($post->post_parent==$pid||is_page($pid)))                 return true;   // we're at the page or at a sub page  else                 return false;  // we're elsewhere }; Usage if (is_tree(2)) {    // stuff }