I currently have linked book topics for Print only, and do it differently from Paul's method of putting a mini-TOC-proxy in the Web version of the book topic (which I like, and may well use one day if I ever get my task list down to single figures). I'm not claiming my way is best, just that it works.
I didn't want Book topics to be linked to any of my web topics - because I had structured my content so that they were always empty apart from the header text. This applied to every book topic in single-sourced PDF/WebHelp content, so I really didn't want to maintain two TOCS, one for each target, and keep them in step.
This means that when you click on the book topic in the WebHelp it doesn't go to any page but just expands/collapses. As Paul says, it does mean breadcrumbs don't work as there is nothing to link to. In my case, I didn't see that was a problem, as my help isn't ginormous.
This is how I did it. In my single-sourced TOC, I linked the book entry to my Print-only header topic (except for one book that is on-line only, and looks exactly like yours with a missing link). Then, in Contents Explorer, I set the Print-Only condition on each header topic file that I didn't want in the WebHelp. You can't do this on a book in the TOC, as that would condition out the book and all the topics in it, which isn't what you want.
That's all good, except there is a bug, although you won't notice it until Flare 10. When Flare builds a target that uses a TOC with linked topics that aren't present for all outputs, it needs the linked topics to be present,
even for the targets that don't use them, or the build will report errors. Under normal circumstances, the topics will be present - that's the whole reason you had to condition them out for the targets that didn't need them. But if you use the new Export Target feature in Flare 10, Flare is clever enough to not export these linked print-only topics, but not clever enough to build the target without them, because the reference to them in the TOC is unconditional, even though they aren't needed eventually. Bug duly raised by the bug queen.
