Composition is a property of Relational Form: relational forms at any depth can be composed side by side into ordered composites.
A composite is an ordered configuration of two or more relational units, held together at a shared Reflexive Sequence to form a structured whole. Composition is what makes composites possible: the capacity to arrange forms alongside each other.
Composition is the second dimension of structure in the derivation. Reflexive Sequence (a property of Relating) provides depth — self-relation going inward, layer by layer. Composition provides breadth — forms arranged alongside each other at any given depth. Together, they give the relational field its first two-dimensional character: things can be both deep (layered through self-relation) and wide (organized alongside each other).