Share the CommonMark grammar, close the guard's hole, refuse the lists no marker spells

src/json-value.ts

@@ -0,0 +1,10 @@
+export type JsonValue = JsonValue[] | boolean | null | number | string | { [key: string]: JsonValue }
+
+export function isJsonValue(value: unknown): value is JsonValue {
+  if (value === null) return true
+  if (typeof value === 'boolean' || typeof value === 'string') return true
+  if (typeof value === 'number') return Number.isFinite(value)
+  if (Array.isArray(value)) return [...value].every(isJsonValue)
+  if (typeof value === 'object') return Object.values(value).every(isJsonValue)
+  return false
+}