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.gorley@gmail.com <mailto:doug.gorley@gmail.com>