Thanks Hraban for your answer, 

> Le 28 nov. 2021 à 15:42, Henning Hraban Ramm via ntg-context <ntg-context@ntg.nl> a écrit :
> 
> Am 28.11.21 um 19:39 schrieb Fabrice L via ntg-context:
>> I have an error when I try to insert a block inside a conditional mode (but there is two nested conditional mode.. is this the problem ?).
> 
> You can’t nest modes in \startmode ... \stopmode.
> I don’t know what are the limitations of \doifmode.

According to the wiki, we cannot nest several \startmode …\stopmode, but there is no limitation with \doifmode.

> 
> Maybe it helps to use additional grouping with {}, \bgroup .. \egroup or \start .. \stop.

Following your advice, I tried with several {}, but no luck. 
> 
>> In my courses notes, I insert some blocks (named «  Complement » in the minimal exemple below) when in « Professor » mode. This works fine, as shown in the first «  \beginComplement … \endComplement  » of my example below.
> 
> Maybe you can work with buffers or (ConTeXt) blocks (the latter were recently discussed here, it’s a quite unknown mechanism).

I already use blocks, but following your message, I tried to think differently. One solution would be to define a block for each course. Something like this (a working minimal example, redone in order this would be more easier to understand (I hope!) what I’m trying to do):

% —————————————
\setuppapersize[S5][S5]
\enablemode[Professor]

\defineblock[ComplementTwo]
\defineblock[ComplementThree]

\setupblock[ComplementTwo,ComplementThree][
	before={\page[yes]\setuppagenumber[state=stop]\setupheadertexts[]\setupbackgrounds[page][background=color,backgroundcolor=red]},
	after={\page[yes]\setuppagenumber[state=start]}]
\starttext

	% Let's process the summaries  ;
	\beginComplementTwo
		Last course, we have seen A.
	\endComplementTwo

	\beginComplementThree
		Last course, we have seen B….
	\endComplementThree

	\beginComplementThree
		Last course, we have seen C….
	\endComplementThree
	% ---- 

	Let's begin course 1. 
	This is course 1 : a lot of pages here about A! 
	\page[yes]
	
	Let's begin course 2. 
	\doifmode{Professor} {
		\useblocks[ComplementTwo]
	}

	This is course 2 : a lot of pages here about B and C! 

	\page[yes]
	Let's begin course 3. 
	\doifmode{Professor} {
		\useblocks[ComplementThree]
	}	

	This is course 3 : a lot of pages here about D... ! 

\stoptext

%————————— 

The only inconvenient of this solution if that I have to define 15 blocks (one for each week of the term): ComplementOne, ComplementTwo, .., ComplementFithteen… Another drawback of this is difficult to move one block form one week to another if I change something. Each block here correspond in fact to a summary of the previous course. So I have typically around 10 pages of summary for each course. The challenge is that the content of each course is not exactly the same form one term to another, so I have to move a page to the summary from one course to the other one, like in a given term, if teach about subject C in course 3 :

	\beginComplementThree
		Last course, we have seen C….
	\endComplementThree

, but next term in course 4:

	\beginComplementFour
		Last course, we have seen C….
	\\beginComplementFour

I have to manually change \beginComplementThree … \endComplementThree to \beginComplementFour … \beginComplementFour.

But I will do this if I do not find another solution. 
Thanks again Hraban.
Fabrice. 

> 
> 
> Hraban
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