allows general addressing forms and pseudo-operations like <code>DIV</code> or <code>MOD</code>
that may not be expressible using a single hardware instruction.
It implements these forms as multiple instructions, often using the <code>R11</code> register
to hold temporary values.
Hand-written assembly can use <code>R11</code>, but doing so requires
being sure that the linker is not also using it to implement any of the other