Organization is a recurring theme in biology, pervading all aspects of life. Inherent in this is a notion of modularity and composition, the idea that at a given level of abstraction, it is possible to decompose a system into a set of building-block components, whose combination confers a specificity of function, and which have some degree of functional independence that allows them to be robustly recombined in different ways.

RNA is a biopolymer composed of a linear sequence of four types of nucleotides, whose pairwise energy-minimizing interactions confer the RNA with a three-dimensional folded structure. To what extent do the sequences and structures of RNA molecules have modular properties?