--- /dev/null
+# namespace http\Client\Curl\Features
+
+CURL feature constants.
+
+> ***NOTE:***
+> These constants have been added in v2.6.0, resp. v3.1.0.
+
+## Constants:
+
+* ASYNCHDNS
+ Whether libcurl supports asynchronous domain name resolution.
+* GSSAPI
+ Whether libcurl supports the Generic Security Services Application Program Interface. Available if libcurl is v7.38.0 or more recent.
+* GSSNEGOTIATE
+ Whether libcurl supports HTTP Generic Security Services negotiation.
+* HTTP2
+ Whether libcurl supports the HTTP/2 protocol. Available if libcurl is v7.33.0 or more recent.
+* IDN
+ Whether libcurl supports international domain names.
+* IPV6
+ Whether libcurl supports IPv6.
+* KERBEROS4
+ Whether libcurl supports the old Kerberos protocol.
+* KERBEROS5
+ Whether libcurl supports the more recent Kerberos v5 protocol. Available if libcurl is v7.40.0 or more recent.
+* LARGEFILE
+ Whether libcurl supports large files.
+* LIBZ
+ Whether libcurl supports gzip/deflate compression.
+* NTLM
+ Whether libcurl supports the NT Lan Manager authentication.
+* NTLM_WB
+ Whether libcurl supports NTLM delegation to a winbind helper. Available if libcurl is v7.22.0 or more recent.
+* PSL
+ Whether libcurl supports the Public Suffix List for cookie host handling. Available if libcurl is v7.47.0 or more recent.
+* SPNEGO
+ Whether libcurl supports the Simple and Protected GSSAPI Negotiation Mechanism.
+* SSL
+ Whether libcurl supports SSL/TLS protocols.
+* SSPI
+ Whether libcurl supports the Security Support Provider Interface.
+* TLSAUTH_SRP
+ Whether libcurl supports TLS Secure Remote Password authentication. Available if libcurl is v7.21.4 or more recent.
+* UNIX_SOCKETS
+ Whether libcurl supports connections to unix sockets. Available if libcurl is v7.40.0 or more recent.