[FT] FTRange "at most"

From section 3.6.3 of the spec:

> If "at most" is specified, then the range is the half-closed interval (unbounded, M].
> 
> 'at most 1' specifies the range (unbounded, 1].

I would assume that neither M or N can be negative, so what does it mean to have "unbounded" for the lower part of the interval?  Does:

	(unbounded,1]

really mean:

	[0,1]

?  If so, why not simply write it that way; if not, then what does it mean?

- Paul