I have been reviewing the Rest Admin API to try to figure out the answer to this question and I may be simply be looking at the wrong documentation.
We're trying to develop an application that will add custom data-driven pages to the site that will take product(s) from multiple selected categories and display them all on a single page, with checkout forms for each. This is done already by other apps, but we have to do a custom implementation so we can match the client's specific functionality needs. An example of an app that does something similar is the Bundle Builder app, which appears to modify the output of {{ content_for_layout }} in the theme.liquid file. It outputs some JSON gathered from the Shopify database (which can be done with the Shopify REST API) and an empty div. Getting the data isn't my concern, but I can't find anywhere in the docs I've looked at where it describes how to modify storefront HTML output.
I suspect it may do this by adding a template (but it has not added that template to the theme files) and associating it with the page URL, or by modifying the output of an existing template, or by adding a section and somehow integrating it with a page, or otherwise, but I have been unable to find documentation for how to do any of those tasks in the docs I've looked at. Other apps appear to add HTML to the storefront as well, such as Privy (which adds pop-ups), Easy Contact Form, and User Photos
What am I missing?
