The only reason why I didn't use liferea instead of rssowl is that I don't know how to select several newsitems for deleting. Because there isn't a "delete all"-functionality I have to select each headline, which loads the content, which is wasted; and by navigating through the list via keyboard I automatically mark other items as read, which is unintended.
Is multiselection possible in liferea, and if yes, how? (and if no, why the...not?)
This feature is not implemented in Liferea for simplicity. Multi-selection causes complex scenarios for all possible headline related menu options.