Say a bit more about iteration

Fixes #66.

infra.bs

@@ -123,6 +123,31 @@ will make the caller automatically rethrow the given value, if any, and thereby
 caller's algorithm. Using prose the caller has the ability to "catch" the exception and perform
 another action.
 
+<h4 id=algorithm-iteration>Iteration</h4>
+
+<p>There's a variety of ways to repeat a set of steps until a condition is reached.
+
+<p class=note>The Infra Standard is not (yet) exhaustive on this; please file an issue if you need
+something.
+
+<dl>
+ <dt>For each
+ <dd><p>As defined <a for=list lt="for each">for lists</a> (and derivatives) and
+ <a for=map lt="for each">maps</a>.
+
+ <dt><dfn export for=iteration lt=while>While</dfn>
+ <dd>
+  <p>An instruction to repeat a set of steps as long as a condition is met.
+
+  <div class=example id=example-while>
+   <p>While |condition| is "<code>met</code>":
+
+   <ol>
+    <li><p>&hellip;
+   </ol>
+  </div>
+</dl>
+
 <p>An iteration's flow can be controlled via requirements to
 <dfn export for=iteration>continue</dfn> or <dfn export for=iteration>break</dfn>.
 <a for=iteration>Continue</a> will skip over any remaining steps in an iteration, proceeding to the