unset behaves in two ways.
If selection is not provided, unset changes the named global setting to a zero or off value.
If a selection is provided, then "unset" undefines object-specific or state-specific settings so that the global setting will be in effect.
unset name [,selection [,state ]]
cmd.unset ( string name, string selection = '', int state=0, int updates=1, int log=0 )