<?php
/*
Plugin Name: Hierarchical Categories
Plugin URI: http://www.pete-b.co.uk/downloads
Description: This plugin makes categories work hierarchically, so if you check a child, all it's parents are checked too
Author:  Pete Bonnett
Version: 0.3
Author URI: http://www.pete-b.co.uk/
*/

//Insert the JS function
function categoryJS() {
    echo "<script type='text/javascript'>
    function initCheckboxes_PSB() {
    if(document.getElementById('categorydiv')) {
        var boxes = document.getElementById('categorydiv').getElementsByTagName('INPUT');
        var isIE = (true && document.attachEvent)?true:false;
        for(var i=0; i<boxes.length; i++){
            if(isIE) {
                boxes[i].attachEvent('onclick', catHierarchy_PSB);
            } else {
                boxes[i].addEventListener('click', catHierarchy_PSB, false);
            }
        }
    }
}

function catHierarchy_PSB(e) {
    var id;
    if(e.target) {
        id = e.target.id;
    } else {
        id = window.event.srcElement.id;
    }
    var elem = document.getElementById(id);
    var isIE = (true && document.attachEvent)?true:false;
    while((elem) && (elem.nodeName == 'INPUT')) {
        if(elem.checked) {
            var pNode;
            if(isIE) {
                pNode = elem.parentNode.parentNode.parentNode.previousSibling.firstChild;
            } else {
                pNode = elem.parentNode.parentNode.parentNode.previousSibling.firstChild.firstChild;
            }
            if(pNode == null) {
                break;
            }
            pNode.checked = true;
            elem = pNode;
        } else {
            break;
        }
    }
}

addLoadEvent(initCheckboxes_PSB);

    </script>";
}

add_action('admin_head', 'categoryJS');

?>