, a bipolar transistor, an amplifier etc. As you can see graphically 
   symbols are built with lines, rectangles, polygons and texts, the graphical primitives shown before.
   In the picture below some components are placed in a schematic window. Components are instances of symbols.
   For example you see three placements of the 'npn' bipolar transistor symbol. 
   Like in C++, where objects are instances of classes, here components are instances of symbols.
  </p>
  <img src="xschem_symbols.png">
  <p>
  