While creating an application template and experimenting with privacy settings, I noticed that when a category has had the "view" permission for anonymous and non-site-member visitors revoked—a situation in which these unauthorized visitors can't see page content in that category and instead see "this page's content is private" or whatever the message is—it is possible to see the full content of that page by clicking on the "view printer-friendly version" button if said button is available (or, theoretically, if there's no button available but you know how to manipulate the URL so that it displays the printer-friendly version of the page).

I was testing this with the access policy set to "closed", but it may also be the case with an "open" policy as well. "Private" blocks all unauthorized users from seeing anything, as expected, and if I leave a button that would ordinarily let them see the printer-friendly page, clicking it just says that the site is private rather than revealing the content.

It's also possible to view source code of pages that should be hidden, whether through the view source option or by looking at a page's revision history, although this is less of a problem if the option buttons/links aren't available because I don't think you can show revisions/source just by manipulating the URL.

In my template's situation it's probably unlikely that anyone unauthorized would find these pages in the first place without help, and I would be recommending that users of this template keep their wikis private anyway, but there are situations in which the wiki may need to temporarily have the policy changed to closed. I've disabled one or both nav menus where appropriate, and non-site-members can't see the usual page options, but there is one category in which I can't disable the nav:side menu and in which that menu has links/buttons for things like viewing history or the printer-friendly page. That category is marked as not viewable by outsiders, but the nav is still there should they find a page in that category. While ideally unauthorized users wouldn't see that nav at all, at least most of the links in that menu, such as the links for editing, tagging and deleting the page, block unauthorized users from performing those functions. The printer-friendly view, history and source view, however, are allowed to go through as normal even when not logged in as an authorized user.

I know about the SUO snippet and will likely use it to help hide the links from those who shouldn't see them; all the same, though, it doesn't stop someone who knows how to view printer-friendly pages via URL from seeing content a wiki owner doesn't want them to see. An unlikely scenario, but one I'd feel better knowing my template's users and I don't have to worry about, if possible.

I'm happy to provide any additional information about this issue should you need it, and welcome suggestions for other ways to circumvent this issue.