CodeMirror through @fastyoke/lang, and the Studio code tab.
Editors
Highlighting today is CodeMirror, through @fastyoke/lang. The playground, and any page that embeds the editor, calls yokeLanguage() from @fastyoke/lang/codemirror.
The Studio code tab shows the app you are designing as source, beside the canvas. The two are the same text. Formatting there is a button, the same contract as yokec fmt: it does not run unless you ask.