This all comes down to bitwise arithmetic.
PKRevealControllerTypeNone has a value of 0 (binary 0000)
PKRevealControllerTypeLeft has a value of 1 (binary 0001)
PKRevealControllerTypeRight has a value of 2 (binary 0010) since 0001 shifted left 1 bit is 0010
PKRevealControllerTypeBoth has a value of 3 (binary 0011) since 0010 | 0001 (or works like addition) = 0011
In context, this is most-likely used to determine a value. The property is & (or bitwise-and) works similar to multiplication. If 1 ands with a number, then the number is preserved, if 0 ands with a number, then the number is cleared.
Thus, if you want to check if a particular controller is specifically type Left and it has a value of 0010 (i.e. type Right) 0010 & 0001 = 0 which is false as we expect (thus, you have determined it is not of correct type). However, if the controller is Both 0011 & 0001 = 1 so the result is true which is correct since we determined this is of Both types.
