MARKEDONLY is a special filtering function that can apply a mark-based filter.

The syntax for MARKEDONLY is as follows:

[BooleanValue := ] Record.MARKEDONLY  
( [SeeMarkedRecordsOnlyBoolean] )

If the optional BooleanValue parameter is defined, it will be assigned a TRUE or FALSE value to tell us whether or not the special MARKEDONLY filter is active. Omitting the BooleanValue parameter, MARKEDONLY will set the special filter depending on the value of SeeMarkedRecordsOnlyBoolean. If that value is TRUE, it will filter to show only marked records; if that value is FALSE, it will remove the marked filter and show all records. The default value for SeeMarkedRecordsOnlyBoolean is FALSE.

Although it may not seem logical, there is no option to see only the unmarked records.

For additional information, refer to the blog entry at https://markbrummel.wordpress.com/2014/03/07/tip-36-using-mark-and-markedonly-in-the-role-tailored-client/.