Returns a lowercased version of EXPR. This is the internal function implementing the \L escape in double-quoted strings.
If EXPR is omitted, uses $_.
What gets returned depends on several factors:
use bytes is in effect:If the current package has a subroutine named ToLower, it will be used to change the case (See "User-Defined Case Mappings" in perlunicode.) Otherwise Unicode semantics are used for the case change.
use locale is in effectRespects current LC_CTYPE locale. See perllocale.
use feature 'unicode_strings' is in effect:Unicode semantics are used for the case change. Any subroutine named ToLower will not be used.