It looks like theThe 'latest' documentation applies for 3.1.0 was published too soongit master branch.
accept() will be added inis ready for the next release of Arduino esp8266. It will be version 3.1.0. Until then you can use server.available(). It works the same way as accept() in ESP8266WiFi library's WiFiServer.
I addedinitiated the addition of server.accept() to, because server.available() in esp8266 WiFiServer works as Ethernet library's server.accept(), not as server.available().