The Web Experience Factory (WEF) Wiki has samples of mobile web applications, including one that leverages the geolocation builder):
The particular input you're asking about determines whether an action is called on the "server" (via AJAX request) when the HTML5 page on the device determines the location, or whether it only calls a Javascript function ( "client" ).
I hope that info helps, ..Mike Burati The postings on this site are my own and do not necessarily represent the positions, strategies, or opinions of IBM.