title: what is meant by "[\x09-\x0d -~]" regular expression?
body: <p>Can any one please tell me what is meant by <code>[\x09-\x0d -~]</code> in the following signature. I am familiar with regular expressions, but this signature is in a C code, and I can not understand what is meant by this <code>x</code> and <code>~</code>, I am trying to make signatures and I am working in java, and I have seen this <code>x</code> and <code>~</code> many times on net, but i could not understand what does it mean. 
  Are these regular expressions or these are hexadecimal value or something else? because i have not seen this neither in regular expressions nor in SIP messages.</p>
  
  <pre><code>^(invite|register|cancel|message|subscribe|notify) sip[\x09-\x0d -~]*sip/[0-2]\.[0-9]
  </code></pre>