The output of ptx

[Dr. David Alan Gilbert]

Hi,
  I could do with a hand understanding the output of ptx.
As input I'm using the two line piece of text:

The penguins like to eat fish at each meal.  Fish must be fresh and
of a variety of species to add some interest to their meal.

If I use the command:

ptx  -S"\n" file

(The full output is later on for those trying to see context)

then the first line of output is:

      like to eat fish at each meal.   Fish must be fresh and    /penguins

I'm trying to understand why '/penguins' is on the end of that; it
appears to be the word that would actually go to the left of the left
piece of text.

Similarly further down I have:

   meal.  Fish must be/          The   penguins like to eat fish at each

And the 'meal.  Fish must be/' seems to be the text that would go to the
right of the rightmost text.

To me it looks like the rule is something like there are 4 pieces of
output on each line:

   a  b   c  d

Where b is the text just before the keyword,
      c is the keyword followed by some text

      a is some text that was after 'c' if there is some spare space on
the left.
      d is some text that would have been before 'b' if there is some
spare space on the right.

This seems confusing - has anyone got a better explanation?

As a by-the-way, the info docs suggest that there is a default ignore
list that should be in '/usr/local/lib/eign'; this doesn't seem to
exist in the coreutils package at all, but I've found a file hanging
around an installation of groff (in /usr/share/groff/1.18.1/eign
on my installation).

Thanks,

Dave

Full output:

      like to eat fish at each meal.   Fish must be fresh and /penguins
   each meal.  Fish must be/           The penguins like to eat fish at
   interest to their meal.        of   a variety of species to add some
          of a variety of species to   add some interest to their meal.
      each meal.  Fish must be fresh   and                     /eat fish at
       The penguins like to eat fish   at each meal.  Fish must be fresh/
       fish at each meal.  Fish must   be fresh and            /like to eat
       /penguins like to eat fish at   each meal.  Fish must be fresh and
   be/          The penguins like to   eat fish at each meal.  Fish must
            The penguins like to eat   fish at each meal.  Fish must be/
         at each meal.  Fish must be   fresh and               /to eat fish
      variety of species to add some   interest to their meal.  of a
   Fish must be/        The penguins   like to eat fish at each meal.
           /like to eat fish at each   meal.  Fish must be fresh and
       to add some interest to their   meal.                    /of species
     to eat fish at each meal.  Fish   must be fresh and /like
   some interest to their meal/        of a variety of species to add
   their meal.          of a variety   of species to add some interest to
   meal.  Fish must be/          The   penguins like to eat fish at each
      of a variety of species to add   some interest to their meal.
   their meal.       of a variety of   species to add some interest to
     species to add some interest to   their meal.              /variety of
   must be/        The penguins like   to eat fish at each meal.  Fish
   .         of a variety of species   to add some interest to their meal
     of species to add some interest   to their meal.            /a variety
   interest to their meal.      of a   variety of species to add some

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