Checking: difference between negative stretch and positive shrink?

[Andreas L Delmelle]

Hi all,
Just wondering about some KnuthSequences for spaces I noticed during  
a debug-session:

glue w=0 stretch=10008 shrink=0
penalty w=0 p=0
glue w=3336 stretch=-10008 shrink=0

What does it mean that the latter glue can be stretched by a negative  
amount?
Why not:
glue w=3336 stretch=0 shrink=10008

Is there a difference as to how the algorithm treats these?


Thanks

Andreas