[Property] Available values [Description] 
If you have specified available values for a parameter, the valid values always appear as a drop-down list. For example, if you provide available values for a DateTime parameter, a drop-down list for dates appears in the parameter pane instead of a calendar control. To ensure that a list of values is consistent among a report and subreports, you can set an option on the data source to use a single transaction for all queries in the datasets that are associated with a data source. Security Note In any report that includes a parameter of data type Text, be sure to use an available values list (also known as a valid values list) and ensure that any user running the report has only the permissions necessary to view the data in the report. For more information, see Security (Report Builder 3.0).