Difference between one glue and two glues after each other

Is there a difference between

A\hskip 1pt \hskip 0pt plus 1fil B


and

A\hskip 1pt plus 1fil B


?

Are these two glues the same in terms of spacing and (line-)breaking? Or do they just add up, as I assume?

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Thanks for both answers! – topskip Aug 30 '10 at 12:23

For spacing and line breaking rules, two glue nodes are exactly the same as one glue except that the algorithms run a little slower. So, the distinction only matters if

• you do node processing with \unskip (or using luatex)
• when the absolute of one of the combined parts would be larger than \maxdimen (in which case you cannot specify the single glue without an error)
• when you parse the output of \showbox somehow.
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That's a much better answer than mine. I didn't even think about points two and three. Thanks! – TH. Aug 30 '10 at 12:14
sorry for the necrology, but would infinite glues change the situation? (i.e. is \hskip 1fil \hskip 1pt Text \hskip -1fil different from \hskip 1fil Text \hskip -1fil?) – Bruno Le Floch Feb 2 '11 at 19:23
@Bruno: that is illegal input. Reverting to valid input, \hskip 0pt plus 1fil \hskip 1pt and \hskip 1pt plus 1fil are indeed treated identical. – Taco Hoekwater Feb 3 '11 at 10:26
thank you for the clarification (I only really know the expansion processor). – Bruno Le Floch Feb 3 '11 at 12:08

They are mostly the same. The difference comes if you put a \unskip before B. In the first case, there will be 1pt of space between the A and B. In the second case, there will be no space.

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I am not putting unskip there :) The source is exactly as above. (Well almost, as I create the nodes by hand in LuaTeX) – topskip Aug 30 '10 at 11:40