A value that can be sent in an HTTP header (User-Agent, X-API-Key, any
defaultHeaders value): non-blank, no C0 control character other than tab, no
DEL, nothing above U+00FF. Node's HTTP layer would otherwise throw an opaque
"Invalid character in header content" 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, X-API-Key, any defaultHeaders value): non-blank, no C0 control character other than tab, no DEL, nothing above U+00FF. Node's HTTP layer would otherwise throw an opaque "Invalid character in header content" 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.