title: why does `^[^[:digit:]]` match a digit and a new line character before the digit
body: <p>In Emacs's regex, why does <code>^[^[:digit:]]</code> match a digit and a new line character before the digit, e.g. it will matches the whole of the second and the third line of</p>
  
  <pre><code>1
  
  1
  </code></pre>
  
  <p>but not the first line.</p>
  
  <p>My original thought is to use <code>^[^[:digit:]]</code> to match a line not starting with a digit. Why does that not work for my purpose? What regex can work for my purpose?</p>
  
  <p>Thanks.</p>