is an option for Dynamic, DynamicModule, Manipulate, and related constructs that specifies an expression to be evaluated when the construct is first displayed.


  • The typical usage is Initialization:>expr.
  • Initialization expressions defined in particular cells in a notebook are evaluated when those cells are first made visible, and not necessarily when the notebook is first opened.
  • Initialization expressions are guaranteed to be evaluated exactly once before the body of the main function is resolved.
Introduced in 2007