{popup} is an integration of overLib, a library used for popup windows. These are used for context sensitive information, such as help windows or tooltips.
{popup_init} must be called only once, preferably within the <head> tag within any page you plan on using the {popup} function.
The path is relative to the executing script or a fully qualified domain path, ie not the relative to the template.
overLib is written and maintained by Erik Bosrup, and the homepage/download is at http://www.bosrup.com/web/overlib/.
XHTML validation: The {popup_init} does not validate with strict and you will get the error document type does not allow element "div" here; (ie a <div> tag in the <head>). This means you will need to include the <script> and <div> tags manually.