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Хранение глобальных настроек для расширений Оперы

The hack: Iframes, error pages, invalid domains and cross-document messaging

The way this works is roughly:

1. When an image is loaded, such as the two example images above, the script creates and injects an iframe pointing to — an invalid URL
2. Next, the other half of the script activates only on the URL mentioned above, and sets up a few listeners for cross-document messages. It recognizes three settings, one for setting Fit to screen, one for no fit, and one for just retrieving the current setting
3. Every 300ms, the iframe will post a message to its parent window, with the current value of the setting.
4. The event listeners in the parent window (the image) will, upon getting a message from the iframe set the correct sizing mode.
5. The net effect of this is that we now have a cross-domain preference storage for UserJS.