code: function use(that, scope, plugin, options) {
  
    // if it's a string then it's either a package name or a script path.
    if (typeof plugin === 'string') {
  
      // use our scope's load() (so it can be overridden)
      plugin = scope.load(plugin, options)
  
      if (plugin.error != null) {
        return plugin
      }
    }
  
    // otherwise, it should be a function, if not, return an error.
    if (typeof plugin !== 'function') {
      return {
        error: 'plugin must be a function'
      }
    }
  
    // it is a function so call it and return the result (may be an error).
    return plugin.call(that, options, that)
  }
docs: the main `use()` function loads the plugin and calls it.