Regexp confusion

Trying to match some numbers, and I'm having some regexp problems. I've
boiled it down to the following:

/* (1) */ select '3.14' similar to E'^\\d+\\.\\d+$'; -- true
/* (2) */ select '3.14' similar to E'^\\d+(\\.\\d+)$'; -- true
/* (3) */ select '3.14' similar to E'^\\d+(\\.\\d+)*$'; -- true
/* (4) */ select '3.14' similar to E'^\\d+(\\.\\d+)?$'; -- false
/* (5) */ select '3.14' similar to E'^\\d+(\\.\\d+)+$'; -- true

So, based on (1) and (2), the pattern '\.\d+' occurs once. So why does
(4) return false? between (3), (4), and (5), it appears as though the
group is matching multiple times.

Thanks,

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*Doug Gorley* | doug(dot)gorley(at)gmail(dot)com <mailto:doug(dot)gorley(at)gmail(dot)com>