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  24 <a name="reordering-in-levels-0-and-1"></a>Reordering in levels 0 and 1</h2></div></div></div>
  25 <p>
  26       Another common operation in the more complex shapers is glyph
  27       reordering. In order to maintain a monotonic cluster sequence
  28       when glyph reordering takes place, HarfBuzz merges the clusters
  29       of everything in the reordering sequence.
  30     </p>
  31 <p>
  32       For example, let us again start with the character sequence (top
  33       row) and initial cluster values (bottom row):
  34     </p>
  35 <pre class="programlisting">
  36       A,B,C,D,E
  37       0,1,2,3,4
  38     </pre>
  39 <p>
  40       If <code class="literal">D</code> is reordered to the position immediately
  41       before <code class="literal">B</code>, then HarfBuzz merges the
  42       <code class="literal">B</code>, <code class="literal">C</code>, and
  43       <code class="literal">D</code> clusters — all the clusters between
  44       the final position of the reordered glyph and its original
  45       position. This means that we get:
  46     </p>
  47 <pre class="programlisting">
  48       A,D,B,C,E
  49       0,1,1,1,4
  50     </pre>
  51 <p>
  52       as the final cluster sequence.
  53     </p>
  54 <p>
  55       Merging this many clusters is not ideal, but it is the only
  56       sensible way for HarfBuzz to maintain the guarantee that the
  57       sequence of cluster values remains monotonic and to retain the
  58       true relationship between glyphs and characters.
  59     </p>
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