
   Document interface
  ====================

  
  What the macro developer write:
  
          .de SH  \" definition of the section heading
          .        po 3n
          .        ll 16n
          ..
          .
          .de PP        \" definition of the paragraph element
          .        po 3n
          .        ll 8n
          ..
          .
          .de QP  \" definition of the quoted paragraph
          .        po 3n
          .        ll 8n
          .        ad r  \" right-align the text
          ..
          .
          .de TR  \" trap macro to set the layout
          .        [... code with conditions and variables ...]
          ..
  
