The control-specification
statements, identified in free-form specifications by the CTL-OPT
operation code, or in fixed-form specificiations by an H in position
6, provide information about generating and running programs. However,
there are three different ways in which this information can be provided
to the compiler and the compiler searches for this information in
the following order:
Control
statements included
in your source 

Once one of these sources is found, the values are assigned and keywords that are not specified are assigned their default values.
See the description of the individual entries for their default values.
The control specification keywords apply at the module level. This means that if there is more than one procedure coded in a module, the values specified in the control specification apply to all procedures.
