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c:geo will register itself for geocaching specific hyperlinks, so that c:geo will be shown as target app, when you click on one of those links in another app.
For example c:geo will register for links starting with
http://coord.info/GC which is e.g. used in mails sent by geocaching.com and target a certain cache listing. Clicking on this link in any app and selecting c:geo as target app, will directly open the cache details of the linked cache in c:geo. The same applies for geocaching related links to other geocaching platforms.