code: 
  package cc.mallet.extract;
  
  import cc.mallet.types.*;
  
  public interface Tokenization extends Sequence //??
  {
    /**
     * Returns the document of which this is a tokenization.
     */
  	public Object getDocument ();
  
    public Span getSpan (int i);
  
  
    /** Returns a span formed by concatenating the spans from start to end.
     *  In more detail:
     *  <ul>
     *   <li>The start of the new span will be the start index of <tt>getSpan(start)</tt>.
     *   <li>The end of the new span will be the start index of <tt>getSpan(end)</tt>.
     *   <li>Unless <tt>start == end</tt>, the new span will completely include <tt>getSpan(start)</tt>.
     *   <li>The new span will never intersect <tt>getSpan(end)</tt>
     *   <li>If <tt>start == end</tt>, then the new span contains no text.
     *  </ul>
     *
     * @param start The index of the first token in the new span (inclusive).
     *   This is an index of a token, *not* an index into the document.
     * @param end The index of the first token in the new span (exclusive).
     *   This is an index of a token, *not* an index into the document.
     * @return A span into this tokenization's document
     */
    Span subspan (int start, int end);
  }
  