Also:
* instead of giving an error message when it lacks permission to read a file (like mousepad) it instead prompts for credentials and attempts to open the file.
* it lets you put the tabs on either side. Or use a panel with a list of open files instead of tabs ("split mode").
Featherpad does have a qt dependency, which may be a dealbreaker for some.
(I am already on KDE so the QT requirement is OK)
EDIT: Tested leafpad. I will keep it around but it doesn't have tabs which I quite like to have. :)
right-click -> Format -> Send selection to...
Also, what does it mean for the text editor to be fast? What speed do you measure?
For a alternative development environment example, the The Glasgow Haskell Compiler is 191.4 MiB by itself and it doesn't have a text editor.
For example Visual Studio Code is 89.6 MiB, but then you have electron25 as a dependency and that is 212.7 MiB extra.
As a somewhat larger example JetBrains bundle it's own customized Jetbrains Runtime JRE with it's 3.5 GiB IDEA IDE.
It's for sure no vim-minimal, but it's pretty lightweight as far as "IDEs" go.
But, even if you add a bunch of Emacs Lisp code, that will put you in the lower 3-digit number of Megabytes. Which would be equivalent to a hello-world Electron app after a lot of optimizations.
The notepad++ plugin ecosystem is a resource that no other software is likely to offer.