A byte sequence of zero or more characters. Strings must be valid UTF-8 sequences. Arbitrary bytes may be encoded by %XX (case insensitive) hex escape sequences. For example:

set resp.http.X-s = "";
set resp.http.X-s = "こんにちは 世界";
set resp.http.X-s = "%F0%9F%8C%AE";

A string may contain the null byte, %00, which has the effect of terminating the string at that point:

set resp.http.X-s = "x%00y"; /* equivalent to "x" */

Literals may be given in a variety of formats, which offer different features:

A string may be not set (as opposed to being set to the empty string), in which case it is considered to have no value. Various functions and operators treat unset strings differently; some render them as the empty string, and some as "(null)". This handling is a property of the function (or operator), rather than a property of the STRING type.

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