Canonical Combining Class - Overlay

Overlay is a specific value that indicates a character is a combining mark designed to be drawn over the base glyph, typically as a strike or horizontal bar, such as in the Latin letter “o” with a slash through it (U+0338). When applied, this combining class does not reorder relative to other combining marks of the same class, meaning the overlay is always positioned directly on top of the preceding base character, without spatial adjustment for diacritics that follow. This ensures that the overlay remains visually stable, acting as a neutral modifier that does not affect the stacking order of other marks, which is crucial for correct rendering of scripts like mathematical notation or phonetic transcription where overlaid lines indicate negation or modification.