Update (Oct. 15 2018):
It’s now waaay easier to control how each of your hyperlinks open.
You don’t have to manually edit the hyperlink URL (as described below).
In version 3.3 of in5, you simply choose the option you want from the Hyperlink panel (in5 > Interactive Widgets).
InDesign has many strengths as an interactive layout tool.
One of its limitations, however, is that it doesn’t let you set a target attribute when creating a hyperlink. The target attribute lets you control how a hyperlink is open.
In this article, I’m going to take you on a deep dive of a new features that we’ve added in in5 version 2.6: Advanced Hyperlink Targeting.
Not only can you use this feature to control links in your web-based HTML, it also gives you a high degree of control in Web Apps, Baker Framework apps, and PhoneGap apps.
If you’re looking for a basic primer on hyperlinks in InDesign, start with this article first.