text: var isFunction = require('../../is-function')
  var config = require('../../config')
  
  module.exports = function sandboxCheck (key, value) {
    if (value === false) { return }
    if (value === true) { return }
  
    if (!Array.isArray(value)) {
      throw new Error('"' + value + '" is not a valid value for ' + key + '. Use an array of strings or `true`.')
    }
  
    if (value.length === 0) {
      throw new Error(key + ' must have at least one value. To block everything, set ' + key + ' to `true`.')
    }
  
    value.forEach(function (expression) {
      if (isFunction(expression)) { return }
  
      if (config.sandboxDirectives.indexOf(expression) === -1) {
        throw new Error('"' + expression + '" is not a valid ' + key + ' directive. Remove it.')
      }
    })
  }
  