That's a bit of legal nitpicking, sorry. CC0 contains something like a
public domain dedication along with a fallback license, so it's neither
entirely. Some call it a "legal instrument". I prefer not calling it
anything.
SPDX doesn't have an official identifier for "public domain", at least
not for the simple "This document is placed into the public domain"
declarations used in some BIPs, see
https://wiki.spdx.org/view/Legal_Team/Decisions/Dealing_with_Public_Domain_within_SPDX_Files
for the rationale provided by their legal team. The rationale is sound,
but It's possible to create "user-defined" identifiers of the form
LicenseRef-X. This is a good idea here to make sure that all SPDX
expression will be formally valid.
And in our case, all "PD" BIPs match the following pseudo regex, so
there's not much potential for confusion:
"This (document|BIP|work|proposal) is (hereby)? (placed)? in the
public domain."
So it makes sense to keep using a single identifier for all of these.
Reading from top to bottom, the passive voice "they become BIP's author or deputy" left me wondering
how it would concretely work in practice. Link to the transferring ownership section for
clarification.
Shareholder refers to an individual or a legal entity owning a share of a company's share capital.
Since the Bitcoin system is not a company, but different actors across the industry have a stake in
its operation, i think the word "stakeholder" better conveys the intended meaning of the original
author here.
