Displayed material, again

[Giuseppe Bilotta <gip.bilotta@iol.it>]

Hello list,

I wish to bring the discussion again on displayed material.
Display material is material that conceptually belongs to a
paragraphs but typographically breaks it. After the display, the
paragraph can continue or not. In ConTeXt, there are many things
which should be considered displayed material: formulas,
enumerations and other itemgroups, quotations, etc. Every
start/stop pair that begins a new paragraph should actually be a
displayed area. In ConTeXt, one can achieve such result by using
[intentnext=yes] or [indentnext=no] on a case-by-case basis,
depending on whether the start/stop pair is supposed to start a
new paragraph or not. Of course, this "manual" way to do the thing
goes against the general principle that the computer is supposed
to do as much of the job as possible, by itself. I therefore wish
to urge Hans to implement a new indentnext option, "auto", which
should give a behaviour similar to the one shown on this example:

=== BEGIN displayed.tex ===

\setupindenting[medium]

\definestartstop[display][before=\initdisplay,after=\terminatedisplay,style=italic]

\def\initdisplay{\ifvmode\else\endgraf\noindent\fi
  \bgroup\advance\leftskip2\parindent\advance\rightskip2\parindent\ignorespaces}
\def\terminatedisplay{\par\egroup\afterassignment\checkifpar\let\ispar=}
\def\checkifpar{\ifx\ispar\par\else\noindent\expandafter\ispar\fi}

\starttext

The purpouse of this document is to practically show how display
material should behave: display material is material that
conceptually belongs to a paragraphs but typographically breaks it
After the display, the paragraph can continue or not.

We now quote Knuth:
\startdisplay
\input knuth
\stopdisplay
and continue the paragraph right after. The following quote will
instead end the paragraph:
\startdisplay
\input tufte
\stopdisplay

This text belongs to a different paragraph: note that it's being
indented (differently from the previous snippet). This paragraph
has no quotations. Instead, the next paragraph will start with
a quotation (display material at the beginning of the paragraph)
and have some text after~it.

\startdisplay
\input knuth
\stopdisplay
is again a quote from Knuth. Observe that this way the source
obeys the \TeX\ convention of empy lines to terminate paragraphs,
and that it is not necessary to manually specify the intentnext
option for the single cases.

\stoptext

=== END displayed.tex ===

The paragraph-wise behaviour of \initdisplay and
\terminatedisplay+\checkifpar (i.e. excluding the left-/rightskip
adaptments, which have only a visual purpouse) should be the
behaviour in case indentnext=auto.

-- 
Giuseppe "Oblomov" Bilotta