ode> should not alter its output further if it is
run twice ("clean&#8594;clean" should be equivalent to "clean"), and
multiple <code>smudge</code> commands should not alter <code>clean</code>'s output
("smudge&#8594;smudge&#8594;clean" should be equivalent to "clean").  See the
section on merging below.</p>
</div>
<div class="paragraph">
<p>The "indent" filter is well-behaved in this regard: it will not modify
input that is already correctly indented.  In this case, the lack of a
smudge filter mea