Here Create a custom loading screen - Babylon.js Documentation

Interfaces must not use “I” prefix.
See Coding guidelines · microsoft/TypeScript Wiki · GitHub

Here Create a custom loading screen - Babylon.js Documentation

Interfaces must not use “I” prefix.
See Coding guidelines · microsoft/TypeScript Wiki · GitHub

It also says to start with

In BJS the convention seems to be to start with I for an interface
Over 200 interfaces all start with I
It’s some strange — use language and dont use him coding style. But okay =)
In no way typescript discourages people to not start an interface with an I. Those are guidelines for people contributing in the typescript project.