 implementation. Many iteration tags will extend this and
 merely implement the <tt>hasNext()</tt> and <tt>next()</tt> methods to provide contents for the handler to iterate
 over.
 </p>

 <p>
 In particular, this base class provides support for:
 </p>

 <ul>
 <li>Iteration control, based on protected <tt>prepare()</tt>, <tt>next()</tt>, and <tt>hasNext()</tt> methods
 <li>Subsetting (<tt>begin</tt>, <tt>end</tt>, <tt>step</tt> functionality, including validation of subset parameters
 for sensibility)
 <li>