A <view> can have an xoffset and a yoffset. These offsets allow the view to be placed relative to the point (xoffset, yoffset). (Otherwise the view is placed using the view's top left corner as a reference point.) If a view has an offset, then
this will effect how layouts position it relative to other views.
The easiest way to see how constantboundslayout works is to contrast it with <constantlayout> as shown here.
The example below shows three views, one with an xoffset value of five. When using just a <constantlayout> the yellow view is shifted left five pixels because of its xoffset.
<canvas height="85">
<view bgcolor="red" >
<view width="80" height="80" bgcolor="yellow" xoffset="5"/>
<view width="60" height="60" bgcolor="silver"/>
<view width="40" height="40" bgcolor="green"/>
<constantlayout axis="x" value="10"/>
</view >
</canvas>
With a constantboundslayout that offset is effectively ignored, meaning only the bounds of the view matters in the layout process. The example below shows all of the subviews now aligned with the use of a constantboundslayout.
<canvas height="85">
<include href="utils/layouts/constantboundslayout.lzx"/>
<view bgcolor="red">
<view width="80" height="80" bgcolor="yellow" xoffset="5"/>
<view width="60" height="60" bgcolor="silver"/>
<view width="40" height="40" bgcolor="green"/>
<constantboundslayout axis="x" value="10"/>
</view >
</canvas>