This is the simplest and most straightforward scheme. The commitment is inserted into the first output OP_RETURN of the witness transaction in the following way:

34-byte_Opret_Commitment =
 OP_RETURN   OP_PUSHBYTE_32   mpc::Commitment>
|_________| |______________| |________________|
  1-byte       1-byte         32 bytes                      

mpc::Commitment is the 32-byte Tagged hash resulting from the MPC tree which is meant to organize RGB client-side data of different contract in one commitment. Hence the size of the total commitment size in the ScriptPubKey is 34 bytes.

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