This would allow wallet operations like funding transactions with smart contract-based inputs such as LN, or any input the Core wallet doesn't know how to sign for.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-933674310
Cat<std::vector<RPCArg>>(
                        {
                            {"add_inputs", RPCArg::Type::BOOL, RPCArg::Default{false}, "If inputs are specified, automatically include more if they are not enough."},
                            {"include_unsafe", RPCArg::Type::BOOL, RPCArg::Default{false}, "Include inputs that are not safe to spend (unconfirmed transactions from outside keys and unconfirmed replacement transactions).\n"
                                                          "Warning: the resulting transaction may become invalid if one of the unsafe inputs disappears.\n"
                                                          "If that happens, you will need to fund the transaction with different inputs and republish it."},
                            {"changeAddress", RPCArg::Type::STR_HEX, RPCArg::DefaultHint{"pool address"}, "The bitcoin address to receive the change"},
                            {"changePosition", RPCArg::Type::NUM, RPCArg::DefaultHint{"random"}, "The index of the change output"},
                            {"change_type", RPCArg::Type::STR, RPCArg::DefaultHint{"set by -changetype"}, "The output type to use. Only valid if changeAddress is not specified. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
                            {"includeWatching", RPCArg::Type::BOOL, RPCArg::DefaultHint{"true for watch-only wallets, otherwise false"}, "Also select inputs which are watch only"},
                            {"lockUnspents", RPCArg::Type::BOOL, RPCArg::Default{false}, "Lock selected unspent outputs"},
                            {"fee_rate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_ATOM + "/vB."},
                            {"feeRate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_UNIT + "/kvB."},
                            {"subtractFeeFromOutputs", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "The outputs to subtract the fee from.\n"
                                                          "The fee will be equally deducted from the amount of each specified output.\n"
                                                          "Those recipients will receive less bitcoins than you enter in their corresponding amount field.\n"
                                                          "If no outputs are specified here, the sender pays the fee.",
                                {
                                    {"vout_index", RPCArg::Type::NUM, RPCArg::Optional::OMITTED, "The zero-based output index, before a change output is added."},
                                },
                            },
                        },
                        FundTxDoc()),
                        "options"},
                    {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR, "psbt", "The resulting raw transaction (base64-encoded string)"},