title: Are line breaks allowed inside html tags?
body: <p>Is it allowed to have a line break inside a html tag? For example:</p>
  
  <pre><code>&lt;h1
  id="heading"&gt;
  </code></pre>
  
  <p>A first test in Chrome shows that this works, but is it specifically allowed by the spec and do all browsers (especially email clients) parse this correctly?</p>
  
  <p>And what about in attributes?</p>
  
  <pre><code>&lt;h1 
  class="one
  two"&gt;
  </code></pre>
  
  <p>In this case, will it be interpreted as a space?</p>
  
  <p>(This last case is not answered in the "possible duplicate question")</p>