Unspendable keys in descriptors

[andrewtoth]

@salvatoshi

This restriction doesn’t quite make sense in the context of wallet policies: it is desired (and expected) that people would use the same xpub in the descriptor with different ‘endings’ for different spending paths (e.g. xpub/<0;1>/*

Apologies for this, I meant restrict to xpub/<m;n>/*. The other optional derivation paths are not allowed.

@salvatoshi

In descriptors, it would need to be decided what to do (or if _ is supported at all) when there are key expressions that are not xpubs.

With the above clarified restriction, that would apply to descriptors as well. A descriptor could only use an xpub in the form xpub/<m;n>/*. This would be a new restriction on both descriptors and wallet policies that implementing this standard would require.