code/models/editablefields/EditableFieldMemberList.php
public function getFieldConfiguration()
    {
        $groupID = ($this->getSetting('GroupID')) ? $this->getSetting('GroupID') : 0;
        $groups  = DataObject::get('Group');

        if ($groups) {
            $groups = $groups->map('ID', 'Title');
        }

        return [
            new DropdownField($this->getSettingName('GroupID'), _t('Moo_EditableField.GROUP', 'Group'), $groups, $groupID),
        ];
    }
public function getFieldConfiguration()
    {
        $groupID = ($this->getSetting('GroupID')) ? $this->getSetting('GroupID') : 0;
        $groups  = DataObject::get('Group');

        if ($groups) {
            $groups = $groups->map('ID', 'Title');
        }

        return [
            new DropdownField($this->getSettingName('GroupID'), _t('Moo_EditableField.GROUP', 'Group'), $groups, $groupID),
        ];
    }
Get extra configuration fields.

@return array