If the library doesn't exist locally in the browser, the page will load in the same way it loads today (and in browsers that don't support this). Because the fe

If the library doesn't exist locally in the browser, the page will load in the same way it loads today (and in browsers that don't support this). Because the feature would only replace known (and working) URLs with a local copy, it's backwards compatible and would continue to work with new versions of the various libraries.