The param object reflects the param element, which passes variable values to ActiveX objects (IE/Windows only), Java applets, and some plugins. Such programs are written to read parameter name/value pairs during initialization so the values are ready to go when the program starts (e.g., the URL of a sound file). IE for Windows commonly assigns a full suite of parameters to some ActiveX controls, even though only a handful might be explicitly defined in the source code. Although properties are read/write, assigning new values after the page has loaded does not convey the new values to the external program.