code: function normalizeChildren (children) {
    return isPrimitive(children)
      ? [createTextVNode(children)]
      : Array.isArray(children)
        ? normalizeArrayChildren(children)
        : undefined
  }
docs: 2. When the children contains constructs that always generated nested Arrays, e.g. <template>, <slot>, v-for, or when the children is provided by user with hand-written render functions / JSX. In such cases a full normalization is needed to cater to all possible types of children values.