Composition Exclusion

Composition Exclusion is a designation applied to certain precomposed characters that are deliberately omitted from the canonical decomposition mapping process, meaning they are not decomposed into base letters plus combining marks even though they technically could be. This exclusion ensures that normalizing text does not force these characters into a different form, preserving their distinct identity for legacy or linguistic reasons. For example, characters like the Croatian digraph dž or the Finnish letter ẅ are excluded so that they remain unchanged during normalization, preventing unexpected reordering or merging with other sequences. This rule helps maintain round-trip compatibility and avoids breaking existing text where these precomposed forms carry specific semantic weight, even though their parts might otherwise be combined. The exclusion list is curated by the standard to balance consistency with practical usage.