Christoph Reller schrieb am 20.12.2020 um 16:15:
> Hi,
>
> The following MNWE uses \dodoubleemptywithset. In ConTeXt MKIV it
> works as expected, In ConTeXt LMTX an error results.

It's a bug, the wrong argument is passed as comma list.

\permanent\tolerant\protected\def\dodoubleemptywithset#1#*[#2]#*[#3]%
   {\doifsomething{#2}%
      {\def\syst_helpers_with_set_step##1{#1[##1][#3]}%
-     \processcommalist[#1]\syst_helpers_with_set_step}}
+     \processcommalist[#2]\syst_helpers_with_set_step}}

\permanent\tolerant\protected\def\dotripleemptywithset#1#*[#2]#*[#3]#*[#4]%
   {\doifsomething{#2}%
      {\def\syst_helpers_with_set_step##1{#1[##1][#3][#4]}%
-     \processcommalist[#1]\syst_helpers_with_set_step}}
+     \processcommalist[#2]\syst_helpers_with_set_step}}

Wolfgang