-import {keymap, highlightSpecialChars, drawSelection, highlightActiveLine, dropCursor,
- rectangularSelection, lineNumbers, highlightActiveLineGutter} from "@codemirror/view"
-import {defaultHighlightStyle, syntaxHighlighting, bracketMatching,
- foldKeymap} from "@codemirror/language"
-import {defaultKeymap, history, historyKeymap} from "@codemirror/commands"
-import {EditorState} from "@codemirror/state"
-
-import {defaultLight} from "./themes";
-
-export function viewer() {
+/**
+ * @param {Element} parentEl
+ * @return {(Extension[]|{extension: Extension}|readonly Extension[])[]}
+ */
+function common(parentEl) {