Often one or more reports that are part of a report book will contain report parameters. The report book is shown as a single document in the report viewer and the parameters area is constructed based on the report parameters defined in all child reports.
Telerik Reporting provides a mechanism known as parameter merging. If the Name and Type of two (or more) parameters from different reports are the same, then they are considered equivalent and are displayed as a single parameter in the viewer's Parameters Area.
When one or more parameters are merged the UI settings of the first one are used for displaying it in the parameters area.
You can control parameter merging via the Mergeable boolean property of the ReportParameter class. The default value of the Mergeable property is true. Set the Mergeable property to false if you want to prevent a parameter from being merged with its equivalent ones.
When Parameters have unique Name properties' values: If a parameter is distinguishable by its Name property, you refer to the parameter directly by the value of its Name property.
When Parameters have repeating Name properties' values but they are not merged: If you need to refer to different reports to set their not-merged parameters with repeating names, you need to use a syntax like reports(<zero-based_index_of_the_report_in_the_ReportBook.ReportSources_collection>).<Parameter_Name> e.g. "reports(0).OrderNumber".
If you do not use the specified syntax and you refer to the report parameter directly by Name property's value, the value will be set only for the first met report parameter matching the given name.
When Parameters have repeating Name properties' and they are merged: If you want to all parameters with the same Name property's value to have the same Value, you need to set their Mergeable property to True. Then you can refer to all parameters at once as a single parameter with an unique Name property's value.