anchor.diff:  -spec listen([{backlog, non_neg_integer()} | {cacertfile, string()}
   	| {certfile, string()} | {ciphers, [ssl:erl_cipher_suite()] | string()}
   	| {ip, inet:ip_address()} | {keyfile, string()} | {nodelay, boolean()}
  -	| {password, string()} | {port, inet:port_number()}])
  +	| {password, string()} | {port, inet:port_number()}
  +	| {verify, ssl:verify_type()}])
   	-> {ok, ssl:sslsocket()} | {error, atom()}.
   listen(Opts) ->
   	ranch:require([crypto, public_key, ssl]),
  
positive.code: 	%% first argument.
  	ssl:listen(0, ranch:filter_options(Opts2,
  		[backlog, cacertfile, certfile, ciphers, ip,
  			keyfile, nodelay, password, port],
  		[binary, {active, false}, {packet, raw},
  			{reuseaddr, true}, {nodelay, true}])).
  
  
negative.code: %%  <dt>password</dt><dd>Optional. String containing the user's password.
  %%   All private keyfiles must be password protected currently.</dd>
  %%  <dt>port</dt><dd>TCP port number to open. Defaults to 0 (see below)</dd>
  %%  <dt>verify</dt><dd>Optional. If set to verify_peer, performs an x509-path
  %%   validation and request the client for a certificate.</dd>
  %% </dl>
  %%
  %% You can listen to a random port by setting the port option to 0.
  