[luatex] unknown control sequences in tex.scantoks

[Esger Renkema]

Dear list,

Running the following program with plain luatex:

-----------------------------------------------------------------
\directlua{ tex.scantoks(0,0,'\string\\unknown \string\\relax') }
\showthe\toks0
\bye
-----------------------------------------------------------------

results in the following:

-----------------------------------------------------------------
This is LuaTeX, Version 1.13.0 (TeX Live 2021/dev)
  restricted system commands enabled.
(./test.tex
> BADunknown \relax .
l.2 \showthe\toks0
-----------------------------------------------------------------

As you see, the backslash preceding the unknown control sequence has 
turned into something confusing. What is this BAD thing? Is this the 
intended behaviour?

Warm regards,
Esger Renkema