<p>
Storage-and-storage instructions such as <code>MVC</code> and <code>XC</code> are written
with the length as the first argument.
For example, <code>XC</code> <code>$8,</code> <code>(R9),</code> <code>(R9)</code> would clear
eight bytes at the address specified in <code>R9</code>.
</p>

<p>
If a vector instruction takes a length or an index as an argument then it will be the
first argument.