doc: dev: Write Plot section.

doc/dev/documentation.org

@@ -602,8 +602,35 @@ creation, this stack is accessible at =self._undo_stack=.
   )
 #+end_src
 
-*** TODO Plot
-*** TODO Mainwindow
+*** Plot
+
+To define a new plot you can create a class who inherit to APlot. The
+creator need threee argument:
+ - A =canvas= of type =MplCanvas=
+ - A =data= used in =draw= and =update= to create and update the plot
+ - A optional =toolbar= of type =PamhyrToolbar=
+This class must implement two method =draw= and =update=, the first
+method to draw the plot from scratch, the second to update the plot if
+data has changed.
+
+#+begin_src python :python python3 :results output :noweb yes
+  from View.Plot.APlot import APlot
+
+  class MyPlot(APlot):
+      def __init__(self, canvas=None, data=None, toolbar=None):
+          super(MyPlot, self).__init__(
+              canvas=canvas,
+              data=data,
+              toolbar=toolbar
+          )
+
+      def draw(self):
+          # Draw function code...
+
+      def update(self, ind = None):
+          # Update function code...
+#+end_src
+
 ** TODO Solver
 
 #+name: graph-pipeline