Re: ConTeXt, XeTeX, ect was Re: OpenType in Windows

[Sanjoy Mahajan <sanjoy@mrao.cam.ac.uk>]

> What does this exactly mean (from wikipedia)?
> "XeTeX works well with both LaTeX and ConTeXt."

XeTeX, PDFTeX, eTeX, and TeX (Knuth's original TeX) are conceptually
at the same level.  The ConTeXt documents (and kpathsea) call this
level the engine.  They all understand basically the same macro
language, the one Knuth described in the _TeXBook_.  

But they have slight differences.  For example, TeX produces DVI
output.  eTeX does too but it adds a few more commands ('primitives')
to the macro language.  PDFTeX produces PDF directly (or can produce
DVI) and has, relative to regular TeX, new macro commands to support
features of PDF; for example, \pdfpagewidth is new to PDFTeX.  Regular
TeX doesn't have an equivalent because the DVI format does not include
a notion of page size.  PDFTeX, from v1.40, also incorporates those
eTeX commands.  And XeTeX has commands to support OpenType, which is
the new standard font format.

LaTeX and ConTeXt are large programs ('macro packages') written on top
of the engine.  Namely, the program -- whether LaTeX or ConTeXt -- is
written in the macro language of the engine.  Most of the program is
independent of the engine, but there are a few changes needed; the
program usually detects which engine is being used underneath it and
adjusts what it does accordingly.

For LaTeX, you choose the engine by the name of the program you run:

* latex    -- uses regular TeX (actually, now it uses PDFTeX pretending
  to be regular TeX)
* pdflatex -- uses PDFTeX
* xelatex  -- uses XeTeX

For ConTeXt, you choose the engine by the '--engine' option to
texexec.  For example: "texexec --engine=pdftex file.tex" will make
you file.pdf.  But as the manual entry now says, you usually do not
need to specify the engine:

       --engine=texengine 
              Specify the program to do the hard work of typesetting.
              Currently either pdftex (the default), xetex, or aleph.
              The luatex value is experimental.  The --engine option
              is not usually needed.  Instead, let texexec figure out
              the setting based on other command-line information.
              See for example the --xetex or --pdf switches.  

So 
* "texexec --xetex file.tex" : uses XeTeX
* "texexec --pdf file.tex"   : uses PDFTeX
* "texexec file.tex"         : also uses PDFTeX (the --pdf option is
                               now the default to texexec)

I hope this explanation clarifies.  If so, you can Wikify (on
wikipedia and/or the ConTeXt wiki)!

-Sanjoy

`Not all those who wander are lost.' (J.R.R. Tolkien)