module.exports = checkFence

function checkFence(context) {
  var marker = context.options.fence || '`'

  if (marker !== '`' && marker !== '~') {
    throw new Error(
      'Cannot serialize code with `' +
        marker +
        '` for `options.fence`, expected `` ` `` or `~`'
    )
  }

  return marker
}