Per the spec, only a BlockContainer" can have line boxes, so let's not
clutter up every Layout::Box with line boxes.
This also allows us to establish an invariant that BFC and IFC always
operate on a Layout::BlockContainer.
Note that if BlockContainer has all block-level children, its line boxes
are not used for anything. They are only used in the all inline-level
children scenario.
Our "frame" concept very closely matches what the web specs call a
"browsing context", so let's rename it to that. :^)
The "main frame" becomes the "top-level browsing context",
and "sub-frames" are now "nested browsing contexts".
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
As well as correctly calculating the height of TableRowBox, this change
calculates the heights of TableRowGroupBoxs also.
As before, this does not correctly take into consideration the 'height'
attribute.
Now the horizontal layout is approximately correct for the
TableRowGroupBoxs we can now see that the `layout_row` method will need
updating to correctly calculate cell width across all rows, not just the
current TableRowGroupBox.
