Expressions in Report Parameters
Report parameters expose AvailableValues, which represents the valid set of value/label pairs that the end user can choose from.
The AvailableValues.ValueMember and AvailableValues.DisplayMember are usually names of columns from the AvailableValues.DataSource, but sometimes you may need to use an expression to combine values from more columns as values/labels/text of the parameters. Expressions are also valid ValueMember/DisplayMembers, for example:
='Mr. ' + Fields.LastName + ', ' + Fields.FirstName
You may also use embedded expressions:
Mr. {Fields.LastName}, {Fields.FirstName}