Creating a mashup project is similar to building a new extension. You need a basic file structure, and as a bare minimum, an HTML file and, for best practices, a separate JavaScript and CSS file. These can either be created manually by moving the code structure to the extension folder or via the Dev Hub, which was explained in Chapter 11, Working with the Qlik Dev Hub.
Unlike extensions, which can be considered to be an add-on to Qlik Sense, where most of the relevant libraries and frameworks are already preloaded, mashups require you to load each required code base manually, which is done via the HTML file.
The mashup template in Qlik Dev Hub comes with absolute positioning and pre-layouts and pre-loads some of the relevant code, which is a good starting point for novices.