按照 Android的文档，我们知道左和顶部的黑线限定，可拉伸区域，以及底部和右侧行中定义的内容区域。

According to the Android documentation, we know that the left and top black line define the stretchable area, and the bottom and right line define the content area.

这很容易理解，但我发现，从机器人-17架构textfield_activated_holo_dark.9.png命名下面的图片。的红颜色在左下方的目的，右下和右上拐角的是什么？

It's easy to understand, but I found the below image named textfield_activated_holo_dark.9.png from android-17 framework. What is the purpose of the red colors in the lower-left, lower-right and top-right corners?

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我相信this线程对同一主题进行一些讨论。

I believe this thread has some discussion on the same topic.

这已经得到的东西做的设置布局界限，我相信它没有记录呢。

This has got something to do with setting layout bounds and I believe its not documented yet.