SWFs, like other documents and media retrieved by a Web browser, are often saved, or cached, locally on the user's hard drive. The next time that media is requested the Web browser may load the file from the cache instead of downloading it over the network. This might be desirable for a Flash movie whose content doesn't change often but undesirable for SWFs that are updated frequently with new content or information.
Using the following techniques, SWFs can be forced to expire immediately from the Web browser's cache or the browser can be forced to re-download the media upon a given time interval.
This is the code that places a SWF file named "main1.swf" into an HTML document: