downcase(*args) public

Returns a copy of str with all uppercase letters replaced with their lowercase counterparts. Which letters exactly are replaced, and by which other letters, depends on the presence or absence of options, and on the encoding of the string.

The meaning of the options is as follows:

No option

Full Unicode case mapping, suitable for most languages (see :turkic and :lithuanian options below for exceptions). Context-dependent case mapping as described in Table 3-14 of the Unicode standard is currently not supported.

:ascii

Only the ASCII region, i.e. the characters “A” to “Z” and “a” to “z”, are affected. This option cannot be combined with any other option.

:turkic

Full Unicode case mapping, adapted for Turkic languages (Turkish, Aserbaijani,…). This means that upper case I is mapped to lower case dotless i, and so on.

:lithuanian

Currently, just full Unicode case mapping. In the future, full Unicode case mapping adapted for Lithuanian (keeping the dot on the lower case i even if there is an accent on top).

:fold

Only available on downcase and downcase!. Unicode case folding, which is more far-reaching than Unicode case mapping. This option currently cannot be combined with any other option (i.e. there is currenty no variant for turkic languages).

Please note that several assumptions that are valid for ASCII-only case conversions do not hold for more general case conversions. For example, the length of the result may not be the same as the length of the input (neither in characters nor in bytes), some roundtrip assumptions (e.g. str.downcase == str.upcase.downcase) may not apply, and Unicode normalization (i.e. String#unicode_normalize) is not necessarily maintained by case mapping operations.

Non-ASCII case mapping/folding is currently supported for UTF-8, UTF-16BE/LE, UTF-32BE/LE, and ISO-8859-1~16 Strings/Symbols. This support will be extended to other encodings.

"hEllO".downcase   #=> "hello"
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