Dear Fabrice,

I tried to compile your example, but not succeed.
I am sorry that I couldn’t tell you what is the problem.

Here is the part of the log file. One thing that I don’t understand is  why it reads ##title and ##number, …
Is it normal in log file?

I hope that experts correct your example to work.

Best regards,

Dalyoung

*****************
tex error       > tex error on line 64 in file mylayout.mkiv: ! Illegal parameter number in definition of \MyHeader

<to be read again> 
t
<argument> ..., foregroundstyle=bold,foregroundcolor=red]{##t
                                                  itle n\high {o}\,##number}...
\dostarttexdefinition ...clf_texdefinition_two {#1
                                                  }
l.64 \stoptexdefinition
                     

54          [{\headerframed[align=middle, foregroundstyle=bold,
55     foregroundcolor=red]
56                {#title n\high{o}\,#number}}]
57     
58        \setupheadertexts
59          [{\headerframed[align=flushleft, foregroundstyle=\ssx]
60              {Lycée JANSON DE SAILLY \\ \date[d=#day,m=#month,y=#year]}}]
61          [{\headerframed[align=flushright, foregroundstyle=\ssx]
62              {#where \\ {#time}}}]
63     
64 >>  \stoptexdefinition
65     
66     \stopenvironment
67     
*********************

A strange thing is that 
> 2017. 8. 19. 오후 7:00, ntg-context-request@ntg.nl 작성:
> 
> Re: About \setupheadertexts : simplify a code