sted in the table above is implemented 
  by the scanner policies.</p>
<p> Three sets of policies govern the behavior of the scanner. These policies 
  make it possible to extend Spirit non-intrusively. The scanner policies allow 
  the core-functionality to be extended without requiring any potentially destabilizing 
  changes to the code. A library writer might provide her own policies that override 
  the ones that are already in place to fine tune the parsing process 
  to fit her own needs. Layers abov