noncombining

Noncombining is a term used in typography and text processing to describe characters that do not participate in combining sequences with adjacent characters. In contrast to combining characters—such as diacritical marks that attach to a base letter—noncombining characters are rendered as independent glyphs or as discrete units within a string. In Unicode, the property is captured by the combining class: characters with a combining class of zero are considered noncombining, while combining marks typically have a nonzero value and modify the glyph of a preceding base character.

Noncombining characters include most Latin letters, digits, punctuation, spaces, and many control codes. They do not automatically attach diacritics to the preceding character; any diacritic that appears above or below a base letter is typically a separate combining mark that must be applied explicitly. When a text contains both base characters and combining marks, rendering engines must place the diacritics in the intended position, if possible, using the combining class information and font rules.

In text processing, recognizing noncombining characters matters for operations such as searching, sorting, and rendering. Unicode normalization forms affect how base characters and combining marks are represented. NFC (Normalization Form Composed) tries to compose sequences into single precomposed characters where available, while NFD (Normalization Form Decomposed) expands them into a base character plus one or more combining marks. Noncombining characters remain unchanged by these processes, aside from their role in forming composed sequences.

Examples of noncombining characters include letters, digits, punctuation, and spaces. Examples of combining marks include the combining acute accent (U+0301) and the combining diaeresis (U+0308).