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Canonical equivalence relates Unicode sequences that represent the same abstract text through canonically interchangeable representations. A precomposed character and its canonical decomposition are an important example. Unicode normalization makes canonically equivalent sequences share a specified normal form.^[ref]

The single code point U+00E9 and the pair U+0065 U+0301 differ in length and stored code units, but represent canonically equivalent accented text. NFD maps both to the decomposed pair, while NFC maps both to the composed character. Comparing raw bytes would miss that relationship if the representations differ. In contrast, the circled digit U+2460 and ordinary 1 have compatibility equivalence without canonical equivalence. Canonical normalization thus preserves more distinctions than the compatibility forms.

Unicode normalization maps text to a specified standard representation while respecting a chosen equivalence relation between Unicode sequences. Canonical normalization uses canonical equivalence; compatibility normalization additionally uses compatibility equivalence. NFD decomposes canonical combinations, NFC then composes where permitted, and NFKD/NFKC additionally apply compatibility decompositions.^[ref]

For example, U+00E9 and U+0065 U+0301 represent canonically equivalent accented text. NFD produces the second sequence from either input, while NFC produces the first. NFKC also changes the circled digit U+2460 to the ordinary digit U+0031; NFC preserves that compatibility distinction. The choice consequently depends on which distinctions an application intends to retain. Unicode normalization is different from choosing a character encoding or a font, and it does not make every visually similar pair of strings equal.