Changes When Lowercased

Changes When Lowercased is a binary character attribute that indicates whether a given character’s lowercase mapping differs from its original code point. In other words, it flags characters that are not already in lowercase form, such as uppercase letters, titlecase letters, or special cases like the Greek final sigma, whose lowercase conversion alters the character itself. This property is used by algorithms that need to determine if a string will change when lowercasing is applied, aiding in case-insensitive comparisons, sorting, and text normalization. It is distinct from simply having a lowercase mapping, as some characters with mappings might not change if their mapping is identical, while others change even if their uppercase form is not typical. The property is derived from the character’s lowercase mapping data and is essential for implementing correct case folding in software.