ConTeXt: using modes to extract only parts of a document

Question

In ConTeXt, is it possible to use modes to extract only parts of a document, say only the exercises?

My naive try was

\defineenumeration[exercise][
before={\startmode[Quest]\blank[line]},
after={\blank[line]\stopmode},
]

\starttext
\input knuth
\startexercise
\input tufte
\stopexercise
\input knuth
\stoptext

but that does not even compile. What I would ultimately like to have:

Running context file.tex I get the full document.

Running context --mode=Quest file.tex I get only the exercises (that are defined in the enumeration exercise).

I would also like, if possible, not have to type \startmode and \stopmode at every instance where the exercises appear.

Answer 1

If you don't mind modifying your source file a little bit, here is a solution using the translate module.

\defineenumeration[exercise]
\usemodule[translate]
\translateinput[startexercise][stopnotmode\startexercise]
\translateinput[stopexercise][{stopexercise\startnotmode[question]}]
\enableinputtranslation


\starttext\startnotmode[question]
Random text
\startexercise
  Content of exercise 1
\stopexercise
More random text
\startexercise
  Content of exercise 2
\stopexercise
More random text
\stopnotmode\stoptext

Note that I have replaced \starttext with \starttext\startnotmode[question] and \stoptext with \stopnotmode\stoptext.

When you compile the file using context test.tex, then the output is:

When you compile using context --mode=question test.tex, then the output is: