[XeTeX] avoiding line break after dash

[Mike Maxwell]

On 12/7/2014 7:14 PM, David Carlisle wrote:
> If adding markup rather than a general setting is acceptable you can use
>
> \mbox{-}abcd

I see that this works--I had not expected it to, so I didn't even try.  What I 
did try was
    \mbox{-abcd}
which certainly worked, but had other drawbacks for my particular situation.

Why does putting the leading dash inside a box prevent a line break between it 
and the following word?
-- 
	Mike Maxwell
	maxwell at umiacs.umd.edu
	"My definition of an interesting universe is
	one that has the capacity to study itself."
         --Stephen Eastmond