fn:lower-case

fn:lower-case($arg as xs:string?) as xs:string

This function is deterministic, context-independent, and focus-independent.

If the value of $arg is the empty sequence, the zero-length string is returned.

Otherwise, the function returns the value of $arg after translating every character to its lower-case correspondent as defined in the appropriate case mappings section in the Unicode standard [The Unicode Standard]. For versions of Unicode beginning with the 2.1.8 update, only locale-insensitive case mappings should be applied. Beginning with version 3.2.0 (and likely future versions) of Unicode, precise mappings are described in default case operations, which are full case mappings in the absence of tailoring for particular languages and environments. Every upper-case character that does not have a lower-case correspondent, as well as every lower-case character, is included in the returned value in its original form.

Case mappings may change the length of a string. In general, the fn:upper-case and fn:lower-case functions are not inverses of each other: fn:lower-case(fn:upper-case($arg)) is not guaranteed to return $arg, nor is fn:upper-case(fn:lower-case($arg)). The Latin small letter dotless i (as used in Turkish) is perhaps the most prominent lower-case letter which will not round-trip. The Latin capital letter i with dot above is the most prominent upper-case letter which will not round trip; there are others, such as Latin capital letter Sharp S (#1E9E) which was introduced in Unicode 5.1.

These functions may not always be linguistically appropriate (e.g. Turkish i without dot) or appropriate for the application (e.g. titlecase). In cases such as Turkish, a simple translation should be used first.

Because the function is not sensitive to locale, results will not always match user expectations. In Quebec, for example, the standard uppercase equivalent of "è" is "È", while in metropolitan France it is more commonly "E"; only one of these is supported by the functions as defined.

Many characters of class Ll lack uppercase equivalents in the Unicode case mapping tables; many characters of class Lu lack lowercase equivalents.

The expression fn:lower-case("ABc!D") returns "abc!d".