Read the block nodes back, and stop a marker change splitting a list

src/markdown/code-language.ts

@@ -0,0 +1,12 @@
+import type { JsonValue } from '../json-value.ts'
+import { carryName } from './opaque-carry.ts'
+import { holdsControlCharacter } from './commonmark-grammar.ts'
+import { holdsEntityReference } from './entity-references.ts'
+
+// spec/flavour.md, The CommonMark blocks: the info string the language rides, `undefined` where the attribute carries it.
+export function fenceInfo(language: JsonValue | undefined): string | undefined {
+  if (language === undefined) return ''
+  if (typeof language !== 'string' || language === '' || language === carryName) return undefined
+  if (/[`\\]/.test(language) || holdsControlCharacter(language) || language !== language.trim() || holdsEntityReference(language)) return undefined
+  return language
+}