Where do you set the "Optional prompt" option in Web Intelligence Rich Client?

The Query Panel is the interface where you create and configure query filters, including prompt filters and their properties. The 'Optional prompt' setting appears within a prompt filter's configuration in the Query Panel, allowing the query to run without requiring the user to supply a value for that prompt.

The Prompts Panel appears at document refresh time to collect user input values; it does not expose configuration options such as making a prompt optional.

The Slice and Dice Panel is used to rearrange and pivot report data after the query has already executed, not to configure query-level prompt properties.

Document Properties controls document-level settings such as auto-refresh behavior and locale, not individual prompt filter configuration.