How can I specify the upper and lower control limits using the 'limits' option within the controlchart command?

I am trying to generate a control chart for a set of data, matlab computes the standard deviation and generates estimated UCL and LCL. In the documented help there is a dot point outlining a limit specifier, detailing its a 3 element column vector which contains the limit values. Could someone clarify how this is used within the command syntax? Thanks!