NSLayoutConstraint
NSLayoutConstraint is a fundamental class in Apple's UIKit and AppKit frameworks used for defining the layout of user interface elements. It represents a single constraint, which is a rule that dictates a relationship between two or more attributes of views. These constraints are the building blocks of Auto Layout, a dynamic view layout system.
A constraint is typically defined by specifying a first item, a first attribute, a relation, a second
When constraints are applied to a view hierarchy, the Auto Layout engine resolves these relationships to determine