Capsules vs corner

Hello everyone! Here is my first newbie question : when a point’s selected, glyph could add a corner. That’s ok.
But when 2 points are selected on a segment, glyph shows me the possibility to add a “capsule” (in french in the text). I would like to know more about this capsule. Is there any tutorial ? What are the difference between corner and capsule ?

Thx you in advance

Those are “cap” components. They work similar to corner components but connecting to two nodes. There is some information in section 8.3 Corner and Cap Components in the Glyphs 2.3 Handbook:

I don’t believe there’s a tutorial for that, yet.

Thank you for your answer : -)
The French translation made me go in the wrong direction!