Allows web sites to register themselves as possible handlers for particular protocols.
window.navigator.registerProtocolHandler(protocol, uri, title);
protocolis the protocol the site wishes to handle, specified as a string.
uriis the URI to the handler as a string. You can include "%s" to indicate where to insert the escaped URI of the document to be handled.
titleis the title of the handler presented to the user as a string.
navigator.registerProtocolHandler("mailto", "https://mail.google.com/mail?view=cm&tf=0&to=%s", "Google Mail");
This creates a handler that allows mailto links to direct the user to Google Mail, inserting the email address specified in the link into the URL.
Specified by the WHATWG's Web Applications 1.0 working draft.
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