This is a set of adjacent controls consisting of a co-ordinate pair and optionally followed by an elevation control.
The controls generally operate independently but can be operated as a group by holding down the 'Ctrl' key when a snap/accept or accept is performed.
On the first co-ordinate control, if the 'Ctrl' key is held down during a snap/accept, the co-ordinates of the second co-ordinate field is set and if applicable the elevation control as well. The function acts as if you performed a snap/accept or accept in each of the three controls simultaneously.
On the second co-ordinate control, if the 'Ctrl' key is held down during a snap/accept, if applicable the elevation control is also set. The function acts as if you performed a snap/accept or accept in each control simultaneously.