This is documented in haproxy's configuration.txt: hdr <string> hdr(header) <string> Note: all the "hdr*" matching criteria either apply to all head

This is documented in haproxy's configuration.txt: hdr <string> hdr(header) <string> Note: all the "hdr*" matching criteria either apply to all headers, or to a particular header whose name is passed between parenthesis and without any space. The header name is not case-sensitive. The header matching complies with RFC2616, and treats as separate headers all values delimited by commas. Use the shdr() variant for response headers sent by the server.