Links and buttons
Links are pretty straightforward. How does this link to the Electric Book website look? That link probably shouldn’t show in the PDF version for print, or it should show in a useful way (like including the link in plain text).
Buttons are trickier. Basically, buttons should be defined by adding a .button class to any element. Ideally the theme allows for inline buttons and block-level buttons:
Again, the print version should have a way to deal with these. Alternatively, the book author can hide buttons in the print version. For instance, themes may support adding a .non-printing class to the element. Or the author can use Liquid control-flow tags, like {% if site.output == "print-pdf" %}, to control whether and how buttons appear in print.