Collapse-Expand all , start all collapsed ?

Good day to you all,
this time i'm building a php generated list of files from a directory.
This part I know. I need to be able to collapse or expand all, as well as start expanded or collapsed ?

Can somebody help me find how to :

1) Collapse - expand all ?
2) Start list closed or open?


Here is my code ?

function Toggle(li) {
var elem = document.getElementById(li);
if(!elem)return; // in case element doesn't exists in document;
elem.style.display = (elem.style.display != "none")? "none": "block";


}

Code (markup):

<div style="position:relative; 
 width:300px;
 height:480px;

 padding:0px;
padding-left:0px; 
padding-top:0px; 
 border-size:1px;
border-color:#000000; 
 overflow:auto;">

<?php
 
$directory = "Art/";
function dirList ($directory)
{
 
    //create 2 arrays - one for folders and one for files
   $folders = array();
   $files = array();
 
    // create a handler for the directory
    $handler = opendir($directory);
 
    // keep going until all files in directory have been read
while (false !== ($file = readdir($handler))) {  
 
        // if $file isn't this directory or its parent,
        // add it to the results array
        if ($file != '.' && $file != '..')
       
        // If file is directory, mark it in bold.
       if(is_dir($directory.$file)) {
        array_push($folders,$file);
		
		    if (time() - filemtime($directory.$file) < 604800) {
    $folder_modified[] = "<span style=\"color:#DB1212;\"><li><div class=\"folder\"><img src=\"plus_icon.gif\"  onclick=\"Toggle('".preg_replace('/\//','_',$directory."".$file)."'); return false;\" /><b>".$file."</b></div>";
} elseif (time() - filemtime($directory.$file) < 31556926) {
    $folder_modified[] = "<span style=\"color:#003366;\"><li><div class=\"folder\"><img src=\"plus_icon.gif\"  onclick=\"Toggle('".preg_replace('/\//','_',$directory."".$file)."'); return false;\" /><b>".$file."</b></div>";
} else {$folder_modified[] = "<span style=\"color:#000000;\"><li><div class=\"folder\"><img src=\"plus_icon.gif\"  onclick=\"Toggle('".preg_replace('/\//','_',$directory."".$file)."'); return false;\" /><b>".$file."</b></div>";}
 
		
       
        // Else not styled
        }else{
        array_push($files,$file);
     $filenamecor = substr($file, 0, -4);
    if (time() - filemtime($directory.$file) < 604800) {
    $file_modified[] = '<span style="color:#DB1212;">'.$filenamecor.'<span>';
} elseif (time() - filemtime($directory.$file) < 31556926) {
    $file_modified[] = '<span style="color:#003366;">'.$filenamecor.'<span>';
} else {$file_modified[] = '<span style="color:#000000;">'.$filenamecor.'<span>';}
 
 
    }
    }
 
    echo "<ul id=\"".preg_replace('/\//','_',substr($directory,0,strlen($directory)-1))."\">\n"; //start a new unordered list for every iteration through dirList
 
$dircor = $directory;
    // tidy up: close the handler
    closedir($handler);
    foreach($folders as $folder=>$file) {
		
      echo "<li id=\"pic\"><div class=\"folder\">".$folder_modified[$folder]."</div>"; //echo the folder name enclosed in a list item
        dirList($directory.$file.'/'); //loop through the contents of $folder
      echo "</li>\n"; //close this list item after all files and folders in $folder have been looped through
   
   
    }
 
    foreach($files as $key=>$file) {

      echo "<li id=\"pic\"><a href=\"index.html\" onclick=\"load('image_view.php?dir=".$dircor."&file=".$file."','boxdisp');return false;\">&nbsp;".$file_modified[$key]."</a></li>\n"; //echo the file name enclosed in a list item
    }
 
 
    echo "</ul>\n"; //close the unordered list
}
 
dirList($directory);
 
?>

</div>

PHP:

Thnaks !