You can control the behavior of the Bourne Again Shell by turning features on and off. Different methods turn different features on and off: The set builtin controls one group of features, and the shopt builtin controls another group. You can also control many features from the command line you use to call bash.
Tip: Features, options, variables, attributes?
To avoid confusing terminology, this book refers to the various shell behaviors that you can control as features. The bash info page refers to them as “options” and “values of variables controlling optional shell behavior.” In some places you might see them referred to as attributes.
The set builtin, when used with the –o or +o option, ...