[texhax] Behavior of \vtop,\vbox, and \vcenter

[Michael Barr]

The funny behavior is clear from the example below:

  $$  \vbox{\hrule height 100pt width 1pt}\eqno(*) $$
  $$  \vtop{\hrule height 100pt width 1pt}\eqno(*) $$
  $$  \vcenter{\hrule height 100pt width 1pt}\eqno(*) $$
              \bye

a plain tex file.  The first one aligns the eqno with the bottom of the 
rule, as expected and the third one aligns it along the center, also as 
expected.  But the second one also aligns it with the bottom, not the top 
of the rule, not as I expect at any rate.  The problem I have is not, of 
course, with rules, but with xy-pic diagrams, but it is evidently not an 
xy-pic problem.  But any solution that involves giving the rules depth 
instead of height is not relevant.

Michael Barr