code: func (t TxWitness) SerializeSize() int {
  	// A varint to signal the number of elements the witness has.
  	n := VarIntSerializeSize(uint64(len(t)))
  
  	// For each element in the witness, we'll need a varint to signal the
  	// size of the element, then finally the number of bytes the element
  	// itself comprises.
  	for _, witItem := range t {
  		n += VarIntSerializeSize(uint64(len(witItem)))
  		n += len(witItem)
  	}
  
  	return n
  }
docs: // SerializeSize returns the number of bytes it would take to serialize the the
  // transaction input's witness.