This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time.
.TP
-.BI "[!] "--mss " "value[:value]"
+.BI "[!] "--mss " value[:value]"
Match a given TCP MSS value or range.