CustomProperty Element (RDL)
Represents a custom property used in a report, report item, or group.
A CustomProperty Name or Value element within a CustomData element with no data rows will evaluate to null if it is based on an expression. Custom properties with expressions that need to be evaluated, even in the case of no rows, should be placed on the CustomReportItem instead.
Client applications using the CustomProperty element should add an application-specific namespace prefix to their custom property names to reduce the likelihood of name collisions in the event that multiple applications are used for editing the same report definition (for example, “msd:FormattedValue” rather than just “FormattedValue”).