title: Why do some valid regular expressions not work with the html5 pattern attribute?
body: <p>See this fiddle: <a href="http://jsfiddle.net/5vTc7/" rel="nofollow">http://jsfiddle.net/5vTc7/</a></p>
  
  <p>If you open the console, you can see that the regular expression in the pattern attribute (<code>(?=^[0-9]*(\.[0-9]+)?$)(?=.*[1-9])</code>) works as expected from JS, but when you enter anything in the input and try to submit, it fails.</p>
  
  <p>In case there's something wrong with my regular expression, I'm simply trying to limit it to numbers greater than 0. I'd like to use the number input (i.e., <code>&lt;input type="number"/&gt;</code>), but I can't, because it doesn't allow you to format the values (e.g., it will display 0.00000001 as 1e-8, which is undesirable).</p>
  
  <p>I am clueless here. Is there something I'm missing? Why doesn't this work?</p>