Fallback value
A parameter required by a landing page can be assigned a value by the caller.
It is possible to list multiple fallback values in sequence. According to the "first match" principle, the fallback value that is the first to return a valid value is used at runtime. Parameter values that are the same for all or at least most of the callers can also be pre-populated with values on the target page.
Here, too, you have the option of specifying an entire chain of fallback values. If the caller does not provide a valid value for the parameter, the target page's fallback value chain is traversed, and the first valid value is used.
If a valid value for a required parameter cannot be determined for either the caller or the target page, the target page cannot be displayed or used.
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