Enclosures in Composition
An enclosure in a composition unifies and ties together specific elements by locking them into simple geometric shapes. For example, in the below painting "The Morning Toilet" by Jean Baptiste Simeon Chardin, notice how the two figures, the woman and child, are combined by enclosing them in simple geometric shapes - the triangle.
Photograph above by Henri Cartier-Bresson demonstrating a triangular enclosure between figures in a composition.
Painting above by Jan van Eyck demonstrating a triangular shape in design.