"draw a bounding box from the framebuffer" misbehaves for Take Element Screenshot

In chapter 17. Screen capture:

Let paint width be the initial viewport’s width – min(rectangle x coordinate, rectangle x coordinate + rectangle width dimension).

Let paint height be the initial viewport’s height – min(rectangle y coordinate, rectangle y coordinate + rectangle height dimension).

Consider a viewport that is 1000px wide, 1000 px tall. We want to take an element screenshot for an element with the following values:
X coordinate: 100
Y coordinate: 100
Width: 400px
Height: 200px

In order to draw a bounding box from the framebuffer, given the above rectangle:

Let paint width be the initial viewport’s width – min(rectangle x coordinate, rectangle x coordinate + rectangle width dimension).
paint width = 1000 - min(100, 100 + 400) = 1000 - 100 = 900
paint height = 1000 - min(100, 100 + 200) = 1000 - 100 = 900

According to step 6 later on, these dimensions are used for the width and height of the resulting canvas. This is not correct. The width should be the width of the element, 400 in this case, not 900. Similarly, the height should be 200, not 900.

For simplicity and correctness, I would advocate for canvas being described as the intersecting area of the viewport and the provided rectangle.

Start with chapter 17, “Screen capture,” and inspect the “draw a bounding box from the framebuffer” algorithm and step 6. Verify how the viewport and rectangle dimensions determine the canvas; done means the specification clearly defines the viewport–rectangle intersection for the resulting canvas.