Do basic calculations
  Use variables
  Use text values
  Use if and else
  Repeat code with loops
  Use functions
  Use callbacks
  Use timers safely
  Create custom dialogs
  Handle dialog results
  Run Python from Expr
  Show output and debug scripts
  Handle missing and invalid values
  Work with arrays and maps
  Use include files
  Use sessions safely
  Use classes in include files
  Use classes to keep data together
  Organize include files
  How relative paths work