I've seen links in web pages on MacOS and IOS that invoke other apps, notably App Store and iBooks. If I recall correctly, they usually have a protocol¹ that in some way identifies the app.
I am using an HTML/PHP/MySQL app called Learning With Texts that allows it to create a URI to a web page with place holders to auto-insert a word to look up in an online dictionary. Now I know that ⌘⌃D can be used on MacOS to display all instances of a string that appear in any MacOS dictionary. I am wondering whether there is a URI syntax that will look it up in a specific dictionary. (And what is that syntax.)
In Catalina, if that matters.
¹the first part of the URI—in a web link, the protocol is “http” or “https”