Another Regex

My brain is starting to get into it, but not quite.

I want to check for a float number, which would accept all of the following:

1
1.1
.1
0 through 999
remove spaces surrounding
return the entire number

it should not accept:
.
letters, etc...

Here's my expression so far:

^\s*((?:[0-9]{1,3}(?:\.[0-9]*)?)|(?:.[0-9]+))\s*$

Here's what I THINK it does--please correct me (since I'm obviously wrong):

EITHER
3 digits, optional decimal by unlimited digits
OR
decimal, unlimited digits

but it accepts 131313. I don't understand why. It shouldn't accept anything larger than 3 digits (999).

Help is appreciated.

Jay

I started with an example from RegexBuddy and fashioned it into this:

/^\s*([0-9]{0,3}(?:\.[0-9]*)?)\s*$/

I then checked outside that that the value wasn't null (which should cause nothing to happen).

I guess I'm getting it a bit more...