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Definitions
<defs> 
 <g>. . . . . . for symbols
  <style>. . .
  <script>. . .
  <gradient id="gradientidentifier">. . .
  <clipPath id="clipidentifier">. . .
  <mask id="maskidentifier">. . .
  <symbol id="symbolidentifier">. . .
  <filter id="filteridentifier">. . .
  <animate id="animateidentifier">. . .
  <text id="textref">. . . for tref
</defs>