A value that can be sent in an HTTP header (User-Agent, any defaultHeaders
value): not blank, no C0 control character other than tab, no DEL, nothing
above U+00FF. Node's HTTP layer would otherwise refuse it at request time, and
a custom transport would receive a CR/LF that injects a header. Checked by char
code so the source stays free of control bytes.
A value that can be sent in an HTTP header (User-Agent, any defaultHeaders value): not blank, no C0 control character other than tab, no DEL, nothing above U+00FF. Node's HTTP layer would otherwise refuse it at request time, and a custom transport would receive a CR/LF that injects a header. Checked by char code so the source stays free of control bytes.