[Xy-pic] What are the default entry modifiers in xygraph, xymatrix, and xymatrix@1?

[Alexander Perlis]

Ross wrote:
> For @1 the code placed is: \vphantom( which effectively adds depth
> to every uppercase and lowercase letter that doesn't have a natural
> descender, and adds height to the shorter lowercase letters.
> 
> Does this explain the apparent extra margins that you observe ?

Unfortunately not, because it's the other way around: \xymatrix@1 has
*smaller* margins than plain \xymatrix. To see this, just examine the
following at 100% in your previewer:

  $X\to x'$ vs $\xymatrix{X\ar[r]&X'}$ vs $\xymatrix@1{X\ar[r]&X'}$

Part of Ross's answer (not copied here --- see his message) indicates
that the smaller margin may be due either to entry modifiers or to a
different value for \objectmargin. Either way, I would like to mimic
Xy-pic's behavior perfectly.

CHALLENGE: using only Xy-pic kernel code, produce results *identical*
to $\xymatrix{X\ar[r]&X'}$ and $\xymatrix@1{X\ar[r]&X'}$.

Help!


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