Logical Order Exception

Logical Order Exception is a character property that defines a small set of scripts, primarily those of South and Southeast Asia, such as Devanagari, Bengali, and Tamil, where the visual order of glyphs does not match the logical order of the underlying text. In these scripts, certain vowel signs and other marks, although typed after a consonant in logical sequence, must be rendered before that consonant on the left side, or repositioned above or below, creating a visual reordering. This property ensures that text shaping engines know which characters to reorder during display, so that stored data remains in a consistent logical form while the on-screen output matches the traditional written appearance. It applies to a limited set of combining marks, typically independent vowel signs and some dependent vowels, and is crucial for accurate rendering, search, and text processing in these languages.