The Application Direct domain implementation provides the simplest way to extend the Web server. It hides the details associated with query data, decoding URL paths, and returning results. All you do is define Tcl procedures that correspond to URLs. Their arguments are automatically matched up to the query data as shown in Example 13-3 on page 179. The Tcl procedures compute a string that is the result data, which is usually HTML. That's all there is to it.
The Direct_Url procedure defines a URL prefix and a corresponding Tcl command prefix. Any URL that begins with the URL prefix will be handled by a corresponding Tcl procedure that starts with the Tcl command prefix. This is shown in Example 18-2: