Pug how to set default class before specifying others in attributes?

Question

Pug

The question arose, how to set the class name for li so that it changes for nested li? Now the class is set for nested lis, but if I write a class separately, then as a result, li gets two classes. And is it possible somehow by analogy to make different classes for the main ul and nested ones?

mixin list(data)
  ul
    each item in data.items
      li(class!=attributes.class)= item.title
        if item.sublevel
          +list(item)(class="into-nav-menu_item")

Answer 1

Used for this purpose the code of the form
but the compiler swears at the number of attributes of the tag.