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I'm writing a tool to streamline some typesetting jobs, and I am having trouble distinguishing between plain Tex and ConTeXt.

LaTeX is straightforward to recognise by the \documentclass command (or \documentstyle for old documents), however I am struggling to find a "smoking gun" to differentiate ConTeXt source from plain TeX source.

It seems that the \starttext . . . \stoptext pair is common in ConTeXt, but not guaranteed. Is there something better, or a combination of things that are better?

I understand that due to TeX's nature it is impossible write a filter to do this 100% accurately, but 90-95% accuracy will still be a great help.

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Any \start... is good enough to identify something as ConTeXt and not Plain, if you do not care about old-school AMSTeX files.

If you want complete commands, there are quite a few top-level document delimiters in ConTeXt:

The usual document delimiters

Special page environments

These create individual pages, but of course such a page may constitute an entire document

  • \startTEXpage — a page that exactly fits the TeX output it contains
  • \startMPpage — a page that exactly fits the MetaPost graphic it contains

Parts of the project system

Other auxiliary files

  • \startmodule — modules and environments are the same, really. In general, though, environments are written ad hoc, while modules are written to be reused (by others).
  • \startxmlsetups — ConTeXt can take XML as input, and a file with XML setups that tell it how to translate the XML to TeX.

Incidentally, LaTeX documents need not contain a {document} environment. LaTeX will generate an error if any output is generated before \begin{document}, which Context does not; but a document without output can still be valid (compile without error), of course. If you access the primitive \end command with \makeatletter\@@end, you can end the document without resorting to LaTeX's \end{document}.

Note from Charles I've made this CW, since by now most of the knowledge it contains comes from the comments below.

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    Not quite true. There are more environments that can delimit the body text from the setup area. These are valid ConTeXt documents: \startdocument FooBar \stopdocument, \startcomponent * FooBar \stopcomponent or \startproduct * FooBar \stopproduct. – Marco May 22 '13 at 7:53
  • @Marco: I'll delete this answer shortly, and maybe undelete it if I fix it. – Charles Stewart May 22 '13 at 7:54
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    Any '\start...' is good enough to differentiate between plain and ConTeXt, if you do not care about old-school amsTeX files. – Taco Hoekwater May 22 '13 at 7:57
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    Apparently he introduced a new command with the same name as the old one a few years later (see beta announcement). – Marco May 22 '13 at 8:47
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    Keep in mind that ConTeXt has a multi-lingual interface. So, if I use the Dutch or the German or the French interface, none of the above commands will be there! – Aditya Jul 3 '13 at 23:11
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FWIW, vim uses the following logic to classify files that have a .tex extension.

  • Ignore all lines at the beginning of the file that start with a comment.
  • Search the next 1000 lines for the following patterns:

    let lpat = 'documentclass\>\|usepackage\>\|begin{\|newcommand\>\|renewcommand\>'
    let cpat = 'start\a\+\|setup\a\+\|usemodule\|enablemode\|enableregime\|setvariables\|useencoding\|usesymbols\|stelle\a\+\|verwende\a\+\|stel\a\+\|gebruik\a\+\|usa\a\+\|imposta\a\+\|regle\a\+\|utilisemodule\>'
    
  • If the file contains either of the patterns, classify it with LaTeX or ConTeXt.

  • Otherwise, classify it as g:tex_flavor (which defaults to plain TeX, but can be overridden by the user).

Source: s:FtTex() function in filetypes.vim

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