任何人都可以请进一步详细说明以下声明
"In this helloworld-example the actions to which access is
controlled are divided in three sections: at the component
level, the category level and the item level"
组件级别访问、类别级别访问和项目级别访问是什么意思。
复制自
http://docs.joomla.org/J2.5:Developing_a_MVC_Component/Adding_ACL#Describing_the_actions_you_want_to_control_the_access_to