ERC-404.. does it exists?

There have been numerous NFT collections launching as hybrid ERC721 / ERC20 (NFTs that can trade also as ERC20’s), they are launching under the pseudonym ERC-404, however, I cannot find that spec (which is kinda funny “404”). Curious if there are any existing specs which cover these hybrid tokens?

I found them super interesting, it provides liquidity outside of traditional NFT marketplaces and I could see these collections taking off.

REF: Pandora, the First Token of ERC-404, Has Zoomed 12,000% As Enthusiasts Latch On to the Experimental Ethereum Standard

There isn’t an ERC404.
The creators haven’t gone through the ERC process but appeared to use the ERC prefix for marketing purposes.

EIP/RIP/ERC numbering changed to sequential from 7500 and is no longer the PR number. Numbers are issued by EIP/RIP/ERC editors/associates.

There was a recent draft ERC with Hybrid functionality: ERC7616: Hybrid Fungible Token