Use this feature to toggle the use of Restrict Chain Selection. When set, (a border highlight indicates it is active) any chain selection will be restricted to the current construction plane. An error message will indicate a selection for the chain is not within the currently set Cplane.
NOTE: This toggle function will effect the Restrict Chain Selection to Cplane setting in Tools>Application Options>Position/Selection>Selection, (by default this setting is checked on but will be unchecked when Restrict Chain Selection is toggled off).

Example Restrict Chain Selection On