static loadCustom(controls) {
    let controlClasses = []
    if (controls) {
      controlClasses = controlClasses.concat(controls)
    }

    // support for user loaded plugin controls
    if (window.fbControls) {
      controlClasses = controlClasses.concat(window.fbControls)
    }

    // loop through each defined custom control.
    // expects a function that receives the master control class to inherit from (or optional classRegister to inherit from subclass)
    // see src/js/control_plugins/ for an example
    if (!this.fbControlsLoaded) {
      for (const loadControl of controlClasses) {
        loadControl(control, control.classRegister)
      }
      this.fbControlsLoaded = true
    }
  }
support dynamic loading of custom control classes
@param {Array} controls