code: def _build_option_description(k):
      
      o = _get_registered_option(k)
      d = _get_deprecated_option(k)
  
      buf = ['{} '.format(k)]
  
      if o.doc:
          doc = '\n'.join(o.doc.strip().splitlines())
      else:
          doc = 'No description available.'
  
      buf.append(doc)
  
      if o:
          buf.append(
              '\n    [default: {}] [currently: {}]'.format(
                  o.defval, _get_option(k, True)
              )
          )
  
      if d:
          buf.append(
              '\n    (Deprecated{})'.format(
                  ', use `{}` instead.'.format(d.rkey) if d.rkey else ''
              )
          )
  
      buf.append('\n\n')
      return ''.join(buf)
docs: Builds a formatted description of a registered option and prints it.