A document source that can be compiled both as plain TeX and Typst (polyglot)

whatisthis

// \begingroup \catcode`\#=12
#let s = ```
 \endgroup \newdimen\pwd \newdimen\pht
 \pwd=160bp \pht=90bp
 \ifnum\ifx\pdfoutput\unDef0\else\pdfoutput\fi>0
  \pdfpagewidth=\pwd \pdfpageheight=\pht \let\os\relax
 \else \def\os{\special{papersize=\the\pwd,\the\pht}}\fi
 \shipout\vbox to\pht{\os \font\ff=cmr10 at 36bp \vskip-1inplus1fil
  \moveleft1in\hbox to\pwd{\hfil\ff \TeX!!\hfil}\vskip1inplus1fil}
 \output{\setbox0\box255\deadcycles=0}\bye
```
#page(width: 160pt, height: 90pt, {
  v(18pt);
  align(center, text(size: 36pt)[Typst]);
})