35a - the parser reads the plain flavour and the lift goes

src/markdown/emit/plain-reduction.test.ts

@@ -118,7 +118,7 @@ test('spells an expand and a nested expand as a folded callout titled by the mar
     '> [!NOTE]- Build log\n>\n> Line.\n>\n> > [!NOTE]- Inner\n> >\n> > Deep.\n',
   )
   assert.equal(plain(node('expand', {}, said('Line.'))), '> [!NOTE]-\n>\n> Line.\n')
-  assert.equal(plain(node('expand', { title: ' *Two*\nlines ' })), '> [!NOTE]- \\*Two\\*\\\n> lines\n')
+  assert.equal(plain(node('expand', { title: ' *Two*\nlines ' })), '> [!NOTE]- \\*Two\\* lines\n')
 })
 
 test('spells a task list as a bullet list whose items lead with their state', () => {

src/markdown/emit/plain-reduction.ts

@@ -190,7 +190,7 @@ function quoted(head: Result<AdfNode[]>, node: AdfNode, reduction: Reduction): R
 
 function reduceExpand(node: AdfNode, reduction: Reduction): Result<AdfNode[]> {
   const title = nodeAttrs(node)['title']
-  const marker = typeof title === 'string' ? `${foldedAlertMarker} ${title.replace(/^[ \t\n\r]+/, '')}` : foldedAlertMarker
+  const marker = typeof title === 'string' ? `${foldedAlertMarker} ${title.replace(/^[ \t\n\r]+/, '').replaceAll('\n', ' ')}` : foldedAlertMarker
   return quoted(paragraphOf([text(marker)], { ...reduction, depth: reduction.depth + 1 }), node, reduction)
 }