Provided by standard library.
Making bistable function blocks dominant:
Q1 = SR (SET1, RESET) means:
Q1 = (NOT RESET AND Q1) OR SET1
The input variables SET1 and RESET as well as the output variable Q1 are type BOOL.
Declaration example
SRInst : SR ;
Example in Function Block Diagram

Example in Structured Text
SRInst(SET1:= VarBOOL1 , RESET:=VarBOOL2 );
VarBOOL3 := SRInst.Q1 ;