Explanation/Reference:
You can add breakpoints to page definition executables and bindings in the page definition editor by
selecting a binding or executable item and using the context menu to toggle or disable 'before' or 'after'
breakpoints on that item. After the application pauses at the breakpoint, you can view the runtime structure
of the objects as well as a list of data for a selected object in the ADF Structure and Data window.
Example: To set and use ADF page definition breakpoints:
In the page definition editor, in the Outline section, right-click the binding or executable you want to set the
breakpoint on. From the context menu, select Toggle Breakpoint Before or Toggle Breakpoint After or both
depending on where you want to place the breakpoint. A blue triangle appears on the item indicating that
the breakpoint has been set.

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References: http://docs.oracle.com/cd/E50457_02/12131/OEPUG/oracle_adf_tools.htm#BEIDGGDC