You can use Mif2Go to create pop-up topics in any of the Help formats.
In this section:
§7.8.1 Understanding pop-up hotspots, links, and topics
§7.8.2 Defining a pop-up hotspot
§7.8.3 Displaying a topic in a pop-up window
7.7.2 Assigning secondary windows for HTML-based Help
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7.8.1 Understanding pop-up hotspots, links, and topics