This allows document.implementation to keep the underlying document
alive for as long as we need it (for example, if someone holds on to a
DOMImplementation JS wrapper after the document is GC'd.)
DOMImplementation.createDocument() should set the content type of the
newly created document, not replace the content type of the
DOMImplementation's own host document.
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 *
