title: Which characters combined with ^ don't need to be escaped in sed?
body: <p>I have checked that <code>^*</code> and <code>^&amp;</code> match lines beginning by <code>*</code> and <code>&amp;</code>, which I didn't since they are special characters. But <code>^[</code> doesn't work. Is this "standard" behavior? Is there any rationale behind this?</p>
  
  <p><code>sed</code> version used was "GNU sed 4.4".</p>