API Reference Guide
The M-Files User Interface Extensibility Framework exposes a number of items that are used to interact with the user interface. Use the navigation on the left to view the various interfaces, enumerations, and events that are available to you.
The easiest way to use this section is to start from the pages under the Overview section on the left. These pages include links to the appropriate interfaces or other references that you need. As an example: the Modules page states that the "OnNewShellUI" method will be passed one argument which is an instance of IShellUI; clicking on the interface name will take you to a section which defines which properties or methods are available within that instance.
Note that many methods within the User Interface Extensibility Framework 2.0 are asynchronous. This is a change from the older User Interface Extensibility Framework approach. You can choose whether to use async functions (and the await keyword), or whether to use a Promise-style syntax, when calling these functions. Examples on this website typically use async functions.