Comparing non-empty string and 0 - is this behavior to be expected?

["Jeremy O'Connor" <jeremyo@xxxxxxxxxxxxxx>]

Looking at the following code

echo ('') ? 'T' : 'F';
echo ('!') ? 'T' : 'F';
echo (0) ? 'T' : 'F';
echo ('' == 0) ? 'T' : 'F';
echo ('!' == 0) ? 'T' : 'F';

the output is:

FTFTT

Is this behavior to be expected?

--
Jeremy O'Connor