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 *
This is because it includes the initial node that the function was
called on, which makes it "inclusive" as according to the spec.
This is important as there are non-inclusive variants, particularly
used in the node mutation algorithms.
For example:
<div>
<input type=radio name=group value=item1 />
</div>
<div>
<input type=radio name=group value=item2 />
</div>
Is a valid DOM and clicking on of these radio buttons should uncheck
the other.
