Nonnegative always includes zero, unless the author had muddled thinking themselves. Since positive is >0 and negative is <0, their negations are nonpositive for <=0 and nonnegative for >=0.
I see your point too, and we're looking forward to a world in which low-power (to enable NFC) open source chips with security features exist. For instance, https://tropicsquare.com is a project that is working towards that.
For now, what we mean by open source hardware is on the one hand that all components are freely available (without NDAs, which nearly all secure elements entail), and on the other that the schematic of the device is open source and passes OSHWA Certification (the CERN license https://ohwr.org/project/cernohl/wikis/Documents/CERN-OHL-ve... is relevant here). This means that you can in principle build a device yourself. The certification will be done post-campaign (we want to avoid copycat products appearing before ours is available in the open market). Like we did with our three previous keys (e.g., https://certification.oshwa.org/us000155.html and https://github.com/solokeys/solo-hw).
Website can distinguish via the optional attestation key.
In terms of features, CTAP v2.1 (https://fidoalliance.org/specs/fido2/) is still draft only, but yes both v1 and v2 keys support hmac-secret and credential management. We could add authnSelection and authnConfig, but not clear if any browsers actually implement/use it.
The actual public key used for logging in to a specific site is completely random.
Optionally, the website can ask for "attestation", which is intended to prove that the public key is from a specific vendor/model. To make this also unlinkable, devices are supposed to share attestation keys in batches of 100k units.
We hope and think that PIV can replace all the practical use cases for PGP. Specifically among those mentioned, `age` for file encryption, and either FIDO resident keys with hmac-secret for password managers, or something like `passage` (fork of `pass` using, again, `age` for encryption). For SSH you can use FIDO for newer OpenSSH, and either `pivy` or `yubikey-agent` via PIV. Cheers!
Specifically, https://google.aip.dev/assets/misc/ebnf-filtering.txt which is a modification of their common expression language https://github.com/google/cel-spec