It returns the remainder of an integer division.
Input  Output 

{"a":1,"b":1}

0

{"a":2,"b":5}

2

{"a":8,"b":3}

2

It can even cope with floats.
Input  Output 

{"a":3.5,"b":2.1}

1.4

{"a":18.25,"b":9}

0.25

{"a":182.7,"b":39.3}

25.5

It can also process negative integers.
Input  Output 

{"a":2,"b":5}

2

{"a":2,"b":5}

2

{"a":2,"b":5}

2
