function to add CSS classname to DW pages baed on namespace, pagename, and namespace depth

pageclass.php

/**
 * compute a list of css class depending on $ID. there are
 * CSS class depending on the pagename, the full pagename,
 * the namespace and the full namespace, and the
 * namespace tree level (root namespace is 0)
 *
 * Those classnames are meant to be used with 'userstyle.css'
 * It would then be easy to create CSS for all start page.
 * or all pages in the :archive namespace could have a special
 * color.
 *
 * namespace classes are prefixed with dwn_. page classes
 * prefixed with dwp_ and tree level are prefixed with
 * dwl
 * namespace separator ':' are converted to '_'
 * '_' in id are doubled in CSS classname. Without this,
 * both "page b in namespace a" 'a:b' and page 'a_b' would
 * get the same css classname.
 *
 * examples :
 * e => dwn_ dwn__ dwl_0 dwp_e
 * _id_with_underscore => dwn_ dwn__ dwl_0 dwp___id__with__underscore
 * c:d:e => dwn_c dwn_c_d dwn_d_ dwl_2 dwp_e dwp_c_d_e
 * c:d_d:e => dwn_c dwn_c_d__d dwn_d__d_ dwl_2 dwp_e dwp_c_d__d_e
 * a:b:c:d:e => dwn_a dwn_a_b dwn_a_b_c dwn_a_b_c_d dwn_d_ dwl_4 dwp_e dwp_a_b_c_d_e
 *
 * @author Schplurtz le Déboulonné
 * @param string $id the full id of a page
 * @return string space separated list of css class name
 */
function pageclass( $id ) {
    if($id{0} == ':')
        $id=substr($id,1);
    $id=str_replace('_', '__', $id);
    $chain = explode(':', $id);
    $pgname = array_pop($chain);
    $classes=Array();

    $classes[]='dwl_'.count($chain);
    $ns='dwn_';
    $classes[]=$ns;
    foreach($chain as $comp) {
        $ns .= "_$comp";
        $classes[]=$ns;
    }
    $parent=array_pop($chain);
    $classes[]="dwn_{$parent}_";
    $classes[]='dwp_'.$pgname;
    if(!empty($parent))
        $classes[]='dwp_'.str_replace(':', '_', $id);

    return implode(' ', $classes );
}