Why value cannot be sent as the User-Agent, or undefined when it can. It is
what a robots.txt rule is matched against and how a parliament's operator finds
us (CONCEPT.md §7), so it may not be blank; and it is a header value, so CR/LF
(header injection), other control characters and anything above U+00FF — which
Node refuses with a raw TypeError mid-request — are refused up front.
Why
valuecannot be sent as the User-Agent, orundefinedwhen it can. It is what a robots.txt rule is matched against and how a parliament's operator finds us (CONCEPT.md §7), so it may not be blank; and it is a header value, so CR/LF (header injection), other control characters and anything above U+00FF — which Node refuses with a raw TypeError mid-request — are refused up front.