title: What sort of binary representation is %xA and such?
body: <p>I'm setting up a websocket server to connect with a web browser, while reading the <a href="https://www.rfc-editor.org/rfc/rfc6455#section-5" rel="nofollow noreferrer">Specification (RFC 6455)</a> for websocket frame exchange I came across these values that are supposed to represent a 4bit op code, they look like this:</p>
  <p>%x0 %x1 %x2 ..... %xA %xB .... %xF</p>
  <p>I know that %x0 = 0000 and %x1 = 0001</p>
  <p>I'd like to know what these values are called and how to convert them to bits.
  Thank you.</p>