How does this awk command work?

How does this awk command work?

The following remarkably terse command will print all of the lines after
the first occurrence of a pattern (including the first occurrence):
awk '/pattern/,0'
Can someone explain how this command works? How does awk parse '/pattern/,0'?
(By the way, I didn't come up with this; it was posted on compgroups.net.)