The shim, once loaded in a device’s browser, opens and maintains a socket connection to the server, according to to Shim’s developers. Shim was written in 2011 by Chris Marstall, Creative Technologist at the Boston Globe. The software has been open sourced. Write the Shim originators on git.hub:
Whenever a new page is requested, the page’s URL is broadcast to all connected browsers, which then redirect themselves to that URL, keeping all devices in sync. Shim info is available on git.hub.