ButtonGroup is used on any instance function, and adds buttons to the inspector organized into horizontal groups.
Use this to organize multiple button in a tidy horizontal group.
[BoxGroup("Titles", ShowLabel = false)]
[TitleGroup("Titles/First Title")]
public int A;
[BoxGroup("Titles/Boxed")]
[TitleGroup("Titles/Boxed/Second Title")]
public int B;
[TitleGroup("Titles/Boxed/Second Title")]
public int C;
[TitleGroup("Titles/Horizontal Buttons")]
[ButtonGroup("Titles/Horizontal Buttons/Buttons")]
public void FirstButton() { }
[ButtonGroup("Titles/Horizontal Buttons/Buttons")]
public void SecondButton() { }