What denotes a comment within an expression rule?

The correct choice signifies that comments within an expression rule are denoted by the syntax used for block comments in many programming languages. Specifically, comments in Appian's expression rules are made by using the block comment notation of /* to start the comment and */ to end it. This allows for more extensive comments that may span multiple lines, making it easier for developers to document their logic or provide context without affecting the execution of the code.

Using this method ensures that any content placed between /* and */ is ignored by the Appian engine during execution, allowing developers to include notes, explanations, or reminders within their expression rules without impacting performance or functionality.

Looking at the other choices, they either use syntax that is incorrect for Appian's expression rules or represent different commenting styles not applicable within this context. For instance, the double forward slash is typically used for single-line comments in some programming languages, while the hash is not a conventional commenting symbol utilized in Appian. Thus, understanding this syntax is crucial for effectively writing and maintaining expression rules within the Appian platform.