A couple of rarely used features of worksheet formulas are Unions and Intersects.

This example illustrates how to use the union and intersect operator (borders below for illustration only) in Excel.
1. The union operator (comma) adds two ranges.

Explanation: the SUM function reduces to =SUM(C4:D8) + SUM(D7:E11), 20.

2. The intersect operator (single space) returns the intersection of two ranges.

Explanation: the SUM function reduces to =SUM(D7:D8), 2.