Substring result short by 1

Hi,

I have a question about substring(), when I run the following query:

prepaid=# select substring('15148300', 0, 5);
substring
-----------
1514
(1 row)

I get a result with only the first 4 characters, not five. Why is
that? The documentation doesn't spend much time discussing the
substring() function and google turned up nothing. I tried
searching the archives but the site is down.

David