DRVL, DRVH, HOPR, LOPR

[Abadie Lana <Lana.Abadie@iter.org>]

Hi all
I have a question regarding the process of DRVL, DRVH, HOPR and LOPR.
By default, there are all equals to 0.

In the EPICS record reference manual, it is written that some checks are performed if these limits are defined.

DRVH  Drive High            If these values are defined then VAL will forced to be in       
                            the range:                                                      
                              DRVL<=VAL<=DRVH                                         
DRVL  Drive Low                                                                             
HOPR  High Operating        These fields determine the upper and lower display limits       
      Range                 for graphics displays and the upper and lower control           
                            limits for control displays. The fields are used by record      
                            support to honor calls to get_graphic_double or                 
                            get_control_double.  If these values are defined,               
                            they must be in the range:                                      
                              DRVL<=LOPR<=HOPR<=DRVH.                              
LOPR  Low Operating                                                                         
      Range     

Questions: 
1. how does one (especially the client) know that the limits are really set? And not default values.
2. if it performs a check that HOPR!=LOPR then what if one defines an upper limit (but does not need a low one) and vice-versa.

Thanks
Lana