Hi Wolfgang,
It is clear, I think I understand (My English is not perfect !). So back to my original post, if I want only the counter is white and surrounded by a red frame, just write :

\defineenumeration
  [ex]
   [text=,
    distance=0.3em,
    width=fit,
    numberconversionset=ACCONVERSION,
    alternative=serried,
   ]

\defineprocessor[ACPROCESSOR][command=\ACFRAME]
\defineconversionset[ACCONVERSION][][ACPROCESSOR->n]

Thanks,
Fabrice

2016-07-22 8:08 GMT+02:00 Wolfgang Schuster <schuster.wolfgang@gmail.com>:
22. Juli 2016 um 02:02
Hi Wolfgang,
In fact, I wanted to know why the instructions to create a new style for the counter were useless (% in the code) .
The settings aren’t useless, the are applied to the counter as intended.

\setupbodyfont[pagella,11pt]

\defineprocessor[ACPROCESSOR][color=red]
\defineconversionset[ACCONVERSION][][ACPROCESSOR->n]

\defineenumeration
  [ex]
  [text=,
   distance=0.3em,
   width=fit,
    numberconversionset=ACCONVERSION,
   alternative=serried]

\starttext

\dorecurse{5}
  {\startex
   \input knuth
   \stopex}

\stoptext
I think I understand that headnumber sends settings (text and number) to the \ACFRAME  command.
The headcommand is applied to the text *and* counter of the enumeration while numberconversionset
changes on the counter, i.e. when you want a frame only around the counter you have to use
numberconversionset but when you want a frame around both you have to use headcommand.

Wolfgang

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