A cache manifest file is a machine-readable file that tells browsers to store web content for an extended period of time. This is useful for creating 'Add to Home Screen' web apps for iOS. When someone loads your Hype document containing a cache manifest file, and then clicks the share button and adds your webpage to their home screen, any assets listed in your cache manifest file will not be downloaded when reopening that home screen app.
Tumult Hype has many built in features for web apps which can be found in the Touch & Mobile chapter of the documentation.
You can have Tumult Hype automatically generate a cache manifest file if you check this box in the Document Inspector:
Here's what a Tumult Hype document containing a single image looks like:
After every re-export, the random string (
#495389812.978265 in this case) will be modified, which will result in an update of assets when the Hype document is reloaded.