Is there a "smoking gun" to distinguish between ConTeXt and plain TeX

Question

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.

Answer 1

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

• \starttext — load the bodyfont and do all the usual setups, plzkthx
• \startdocument — used for parametrising documents. See Abstracting an author list.

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

• \startcomponent — (reusable) product elements
• \startproduct — a product contains multiple components
• \startenvironment — setups and definitions
• \startproject — link products and components to suitable environments

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.

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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.

Answer 2

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