islowerlike

islowerlike is a term used in text processing to describe a property of strings related to lowercase forms. In its general sense, a string is considered lowerlike if every alphabetic character that has a lowercase form appears in lowercase within the string. Non-letter characters are usually ignored when evaluating the property.

Formally, for a string s, islowl ike(s) is true if for every code point c in s, if c has a lowercase mapping then tolower(c) equals c. Characters without a case mapping are typically ignored. Some definitions require at least one letter to be present, while others allow the empty string or strings containing only non-letter characters to be considered lowerlike.

Relation to standard predicates: isl ow erlike is related to existing lowercase checks such as islower or tolower, but it is not a universal standard across languages. Where islower tests a single character, isl ow erlike describes a string-level property that may incorporate Unicode-aware case mappings and ignore non-alphabetic code points. Implementations often rely on Unicode data to determine which code points have lowercase mappings and to compare them accordingly.

Use cases and limitations: The predicate can be useful in input validation for identifiers that must be lowercase, in case-insensitive matching schemes that require strict lowercase input, or in normalization workflows. Limitations include locale-dependent mappings (for example, certain languages handle letter case differently), characters with special casing (such as digraphs and ligatures), and performance considerations for large texts. In Unicode-aware environments, the definition is clearer when using standardized mappings like Unicode's lowercase mapping and casefold operations.

See also: islower, tolower, casefold, Unicode property Lowercase_Letter.