text: 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
  }
  