Am 03.07.2012 um 18:04 schrieb luigi scarso:

> 
> 
> On Tue, Jul 3, 2012 at 5:27 PM, Alan BRASLAU <alan.braslau@cea.fr> wrote:
> > On Tue, 3 Jul 2012 15:48:43 +0200
> > Hans Hagen <pragma@wxs.nl> wrote:
> >
> >> It's a rather (old) low level boxing macro ...
> >>
> >> \start
> >>      \showboxes
> >>      \centerbox width 10cm height 3cm {Alan is surprised}
> >> \stop
> >
> > My TeX culture remains, alas, always limited (even if I have the
> > TeXbook on my office bookshelf, indeed \centerbox does not appear in
> > plain TeX). Nothing in the ConTeXt manual, either. Of course, a
> > leisurely browsing of the source code would reveal many such treasures!
> There is also \vcenter
> 
> \starttext
> xxxxxxxxxxg\ruledvbox{\hsize=5cm\vcenter to 3cm{Alan is surprised}}gxxxxxxxxx \type{\vcenter}\par
> xxxxxxxxxxg\ruledvbox{\centerbox width5cm height3cm{Alan is surprised}}gxxxxxxxxx \type{\centerbox}\par
> xxxxxxxxxxg\ruledvbox{\vcenter{\centerbox width5cm height3cm{Alan is surprised}}}gxxxxxxxxx\type{\centerbox+\vcenter}\par
> \stoptext
> 
> (\vcenter is a TeX primitive)

ConTeXt redefines \vcenter because the primitive can only be used in math mode.

Wolfgang