Required changes

Changes in class definition

Theme class definition uses now a different syntax:
Instead
  class Theme extends BaseTheme {you should use
  class Theme_<i>themename</i> extends BaseTheme {where themename is name of your theme in lowercase.

Changes in function header()

• Function header() takes now an optional parameter $title.
  Instead
    function header() {you should use
    function header($title = "") {
• Previously all pages in Drupal site had the fixed page title: sitename - site slogan. Now the page title can be dynamic - for example when displaying single node, the page title can be note title - sitename. So, instead
    print variable_get("site_name", "drupal") ." - ". variable_get("site_slogan", "");you should use a more complex syntax:
  
    if ($title) {                                                                          
    print $title ." - ". variable_get("site_name", "drupal");                            
  }                                                                                      
  else {                                                                                 
    print variable_get("site_name", "drupal") ." - ". variable_get("site_slogan", "");   
  }
  of if you want to use compact version of the same construction:
  
    print $title ? $title." - ". variable_get("site_name", "drupal") :         
variable_get("site_name", "drupal") ."  ". variable_get("site_slogan", "");
  This piece of code checks if $title is present. If yes, it outputs $title and site name, if not, it outputs site name and slogan.
• If you used theme_account() function (what outputs login/membership box) in header(), please remove it. Login box placement is controlled in Administration > blocks page from now on and theme_account() is no longer used.

Changes in function node()

• format_name() accepts now parameter $node, not $node->name. Also $node->timestamp is replaced with $node->created. So, instead   print strtr(t("Submitted by %a on %b"), array("%a" => format_name(<b>$node->name</b>), "%b" => format_date(<b>$node->timestamp</b>)));you should use
    print strtr(t("Submitted by %a on %b"), array("%a" => format_name(<b>$node</b>), "%b" => format_date(<b>$node->created</b>)));
• node_index() is no longer used because Drupal 4.0 has more sophisticated classification system than Drupal 3.0 meta tags. So instead plain simple
    print node_index($node);you have to use
  
    $terms = array();                                                                           
 
  if (function_exists("taxonomy_node_get_terms")) {                                           
    foreach (taxonomy_node_get_terms($node->nid) as $term) {                                  
      $terms[] = l($term->name, array("or" => $term->tid), "index");                            
    }                                                                                           
  }

  print $this->links($terms);
• Function link_node() accepts an optional parameter $main. Instead
  
    if ($main) {
    print $this->links(link_node($node));
  }
  you should use
  
    if ($links = link_node($node, $main)) {                                                     
    print $this->links($links);
  } </li></ul><h2>Changes in function comment()</h2>
<ul><li>format_name() accepts now parameter $comment, not $comment->name. Instead
<code>  print strtr(t("Submitted by %a on %b"), array("%a" => format_name(<b>$comment->name</b>), "%b" => format_date($comment->timestamp)));
  you should use
    print strtr(t("Submitted by %a on %b"), array("%a" => format_name(<b>$comment</b>), "%b" => format_date($comment->timestamp)));

Changes in function footer()

• If you used theme_account() function (what outputs login/membership box) in footer() function, please remove it. Login box placement is controlled in Administration > blocks page from now on and theme_account() is no longer used.

Optional changes

New function: system()

• Optionally theme can have a system() function what provides info about theme and its author:
  function system($field) {
  $system["name"] = "theme name";
  $system["author"] = "author name";
  $system["description"] = "description of the theme";
  return $system[$field];
  }