title: SVG path arc radius ratio
body: <p>All the docs I've seen for the ArcTo instruction for a SVG <code>&lt;path/&gt;</code>'s <code>d</code> attribute give the first two arguments as the x and y radius of the arc. </p>
  
  <p>Earlier, though, I was playing around, and in FF8 and Safari 5, it seemed like the path</p>
  
  <pre><code>&lt;path d="M 100 100 A 50 50 0 0 0 200 100 Z"/&gt;
  </code></pre>
  
  <p>and the path</p>
  
  <pre><code>&lt;path d="M 100 100 A 1 1 0 0 0 200 100 Z"/&gt;
  </code></pre>
  
  <p>rendered identically.  From a bit more playing it seemed like what was really being used was the ratio between <code>rx</code> and <code>ry</code>.  This makes sense (since what else are you going to do if the current position is more than <code>2r</code> away), but is it officially documented anywhere?  </p>
  
  <p>It'd be nice if I could rely on this behaviour so I didn't have to manually calculate the x and y radius and instead just state their ratio.</p>