How to programmatically execute xcm message from Patachain A to execute an extrinsic on Parachain B

Question

I have a local relaychain setup with 2 parachains Parachain A and Parachain B . I will like to execute an XCM message from Parachain A to execute an extrinsic on Parachain B using the Transact instruction.How do I achieve this programmatically without using polkadot.js webapp. Do I need to add pallet-xcm as a dependency , then write code in Parachain A to create the instruction and then call send which is on pallet-xcm? Is there any sample code that does this or detailed instruction on this or programmatically executing xcm?

// UPDATE

When sending Transact XCM Instruction from parachain A, how do I specify (or how does the xcm-executor know) the pallet / pallet id on the target Parachain B which contains the extrinsic to be executed, or is it not required?

for example. The following Transact Xcm message is sent from parachain A to execute an extrinsic called ping defined in the cumulus-ping pallet on Parachain B. In the xcm message below, I do not see the cumulus-ping pallet or the index of the cumulus-ping pallet specified in the XCM instruction. so how does XCM determine the pallet / module where the ping extrinsic on Parachain B is located? The code I attached below is from the cumulus repo here

// This is Parachain A, which sends the xcm message

send_xcm::<T::XcmSender>(
                    (Parent, Junction::Parachain(para.into())).into(),
                    Xcm(vec![Transact {
                        origin_kind: OriginKind::Native,
                        require_weight_at_most: Weight::from_parts(1_000, 1_000),
                        call: <T as Config>::RuntimeCall::from(Call::<T>::ping {
                            seq,
                            payload: payload.clone().to_vec(),
                        })
                        .encode()
                        .into(),
                    }]),
                ) 

// This is the runtime of patachain B which contains cumulus-ping pallet which has the ping extrinsic

construct_runtime! {
    pub enum Runtime where
        Block = Block,
        NodeBlock = generic::Block<Header, sp_runtime::OpaqueExtrinsic>,
        UncheckedExtrinsic = UncheckedExtrinsic,
    {
        System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
        ...
        Spambot: cumulus_ping::{Pallet, Call, Storage, Event<T>} = 99,
    }
}

Answer 1

There are no detailed instructions explaining how to use transact, but there is an demo article by OAK network that explains the working of XCMP and in that they have used cumulus_ping that is using transact instruction here. It helped me a lot in understanding the working of transact instruction I hope it helps you too.