The following is present in the entry of client/Click(), at the bottom:
"Note that due to network lag, it is possible when clicking on moving objects for the location of those objects to have changed by the time the Click() proc is executed. That is the reason for the Location argument. It tells you where the click originally took place."
I think it should really also be present in atom/Click(), because it's very likely that users of the former won't always check the entry of its caller (client/Click()).
(( Also thinking about it, atom/Click() should really be named atom/Clicked() >_> ))
(EDIT: all of the above also applicable for DblClick())
EDIT2: Also, in the reference, the entry for the 'block' proc is named 'block', instead of the "traditional" 'block proc'. This may falsely indicate at first, that there is a type object /block.