Copy moveLineUp/moveLineDown command from Codemirror source into move-lines.js. Plan is to modify them to fix issue when moving the only line from a a single line block. When that happens it results in the following text data in the buffer:

∞∞∞text
∞∞∞text

And the separator needs a newline on both sides to be valid

src/editor/block/commands.js

@@ -7,6 +7,9 @@ import {
 import { heynoteEvent, LANGUAGE_CHANGE } from "../annotation.js";
 import { blockState, getActiveNoteBlock, getNoteBlockFromPos } from "./block"
 import { levenshtein_distance } from "../language-detection/levenshtein"
+import { moveLineDown, moveLineUp } from "./move-lines.js";
+
+export { moveLineDown, moveLineUp }
 
 
 export const insertNewBlockAtCursor = ({ state, dispatch }) => {
@@ -60,21 +63,6 @@ export const selectAll = ({ state, dispatch }) => {
     return true
 }
 
-/**
- * Prevent moveLineUp from executing if any cursor is on the first line of the first note
- */
-export function moveLineUp({ state, dispatch }) {
-    if (state.readOnly)
-        return false
-    if (state.selection.ranges.some(range => {
-        let startLine = state.doc.lineAt(range.from)
-        return startLine.from <= state.facet(blockState)[0].content.from
-    })) {
-        return true;
-    }
-    return defaultMoveLineUp({state, dispatch})
-}
-
 
 export function changeLanguageTo(state, dispatch, block, language, auto) {
     if (state.readOnly)

src/editor/block/move-lines.js

@@ -0,0 +1,73 @@
+import { EditorSelection } from "@codemirror/state"
+import { blockState } from "./block"
+
+
+function selectedLineBlocks(state) {
+    let blocks = [], upto = -1;
+    for (let range of state.selection.ranges) {
+        let startLine = state.doc.lineAt(range.from), endLine = state.doc.lineAt(range.to);
+        if (!range.empty && range.to == endLine.from)
+            endLine = state.doc.lineAt(range.to - 1);
+        if (upto >= startLine.number) {
+            let prev = blocks[blocks.length - 1];
+            prev.to = endLine.to;
+            prev.ranges.push(range);
+        }
+        else {
+            blocks.push({ from: startLine.from, to: endLine.to, ranges: [range] });
+        }
+        upto = endLine.number + 1;
+    }
+    return blocks;
+}
+
+function moveLine(state, dispatch, forward) {
+    if (state.readOnly)
+        return false;
+    let changes = [], ranges = [];
+    for (let block of selectedLineBlocks(state)) {
+        if (forward ? block.to == state.doc.length : block.from == 0)
+            continue;
+        let nextLine = state.doc.lineAt(forward ? block.to + 1 : block.from - 1);
+        let size = nextLine.length + 1;
+        if (forward) {
+            changes.push({ from: block.to, to: nextLine.to }, { from: block.from, insert: nextLine.text + state.lineBreak });
+            for (let r of block.ranges)
+                ranges.push(EditorSelection.range(Math.min(state.doc.length, r.anchor + size), Math.min(state.doc.length, r.head + size)));
+        }
+        else {
+            changes.push({ from: nextLine.from, to: block.from }, { from: block.to, insert: state.lineBreak + nextLine.text });
+            for (let r of block.ranges)
+                ranges.push(EditorSelection.range(r.anchor - size, r.head - size));
+        }
+    }
+    if (!changes.length)
+        return false;
+    dispatch(state.update({
+        changes,
+        scrollIntoView: true,
+        selection: EditorSelection.create(ranges, state.selection.mainIndex),
+        userEvent: "move.line"
+    }));
+    return true;
+}
+
+/**
+Move the selected lines up one line.
+*/
+export const moveLineUp = ({ state, dispatch }) => {
+    // prevent moving lines up before the first block separator
+    if (state.selection.ranges.some(range => {
+        let startLine = state.doc.lineAt(range.from)
+        return startLine.from <= state.facet(blockState)[0].content.from
+    })) {
+        return true;
+    }
+    
+    return moveLine(state, dispatch, false)
+}
+
+/**
+Move the selected lines down one line.
+*/
+export const moveLineDown = ({ state, dispatch }) => moveLine(state, dispatch, true);

src/editor/keymap.js

@@ -1,7 +1,7 @@
 import { EditorView, keymap } from "@codemirror/view"
 import { EditorSelection } from "@codemirror/state"
 import { indentWithTab, insertTab, indentLess, indentMore, undo, redo } from "@codemirror/commands"
-import { insertNewBlockAtCursor, addNewBlockAfterCurrent, moveLineUp, selectAll, gotoPreviousBlock, gotoNextBlock, gotoPreviousParagraph, gotoNextParagraph } from "./block/commands.js";
+import { insertNewBlockAtCursor, addNewBlockAfterCurrent, moveLineUp, moveLineDown, selectAll, gotoPreviousBlock, gotoNextBlock, gotoPreviousParagraph, gotoNextParagraph } from "./block/commands.js";
 
 export function heynoteKeymap(editor) {
     return keymap.of([
@@ -11,6 +11,7 @@ export function heynoteKeymap(editor) {
         ["Mod-Shift-Enter", insertNewBlockAtCursor],
         ["Mod-a", selectAll],
         ["Alt-ArrowUp", moveLineUp],
+        ["Alt-ArrowDown", moveLineDown],
         ["Mod-ArrowUp", gotoPreviousBlock],
         ["Mod-ArrowDown", gotoNextBlock],
         ["Ctrl-ArrowUp", gotoPreviousParagraph],