清单2显示了一个定制事件例子，它展现一个Atom提要中的图标元素。
Listing 2 shows an example of a custom event that represents the icon element in an Atom feed.
如果要对某个图标元素添加注释，就可以使用点画线将其连接到该元素。
To relate the comment to whatever diagram elements it is about, connect them with dashed lines.
通过单击文件夹图标可以折叠某个元素组。
You can collapse a grouping of primitives by clicking the folder icon.
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