Handles to Objects
A handle is a pointer to a variable, function, module, or other object. Using a handle lets you write variables or functions that work with the object itself, for example to access its attributes — instead of just its value which is what you usually get when you mention a variable by identifier in an expression.
In a table result, a handle in an index or content cell usually shows the title of the object. If you select Show by identifier from the Object menu (or press Control+y) it toggles to show identifiers instead of titles (as it does in the node diagrams). If you double-click a cell containing a handle (title or identifier) it opens its Object window (as it does when you double-click a node in a diagram).
Attributes that contain handles
The attributes, inputs, outputs, and contains (the list of objects in a module) each consist of a list of handles to objects. The attribute isIn is a single handle to the module that contains this object — the inverse of contains.