As a best practice, pass data into the application by using parameters, and reference those parameters instead of top-level pages. When you request values for the parameters, a new instance of the data page loads for each distinct value of each parameter you requested. Referencing values from other top-level pages during the loading process loads stale data because the data page does not refresh when those properties change.
If you need to load data from top-level pages, you can use the Pages & Classes tab. For example, if you are loading a data page asynchronously and need data from other top-level pages, you must list those pages on the Pages & Classes tab of the data page.
For more information, see Defining the pages and classes of a rule.