Floats should not overlap atomic elements

[liZe]

In CSS 2.1:

The border box of a table, a block-level replaced element, or an element in the normal flow that establishes a new block formatting context (such as an element with 'overflow' other than 'visible') must not overlap the margin box of any floats in the same block formatting context as the element itself.

They currently overlap:

<style>
  div {
    float: right;
    background: #f004;
    width: 50%;
    height: 10em;
    margin: 1em;
  }
  h1 {
    border: 1px solid black;
    overflow: hidden;
  }
</style>
<div>float</div>
<h1>title</h1>