The BITTEST() function tests the state of a specified bit in an integer value.
The BITTEST() function converts expr to a 32 bit integer and tests the state of the bit identified by bit, returning True if it is set and False if it is reset. Bits are numbered from 0 to 31 from the least significant end of the value. The effect of this function with a bit value outside this range is undefined.
IF BITTEST(FLAGS, 2) THEN DISPLAY(IT$CS) :
This statement clears the screen if bit 2 is set in the FLAGS variable.