blog: add IRC CHGHOST capability spec (#99)

This is from 2013. It is quite possibly one of my oldest writings on
the internet.

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+---
+title: "IRCv3.2 CHGHOST Extension"
+date: "2013-10-04"
+---
+
+# IRCv3.2 CHGHOST Extension
+
+The chghost client capability allows a server to directly inform clients about a
+host or user change without having to send a fake quit and join. This capability
+MUST be referred to as `chghost` at capability negotiation time.
+
+When enabled, clients will get the CHGHOST message to designate the host of a
+user changing for clients on common channels with them.
+
+The CHGHOST message is one of the following:
+
+    :nick!user@host CHGHOST user new.host.goes.here
+
+This message represents that the user identified by nick!user@host has changed
+host to another value. The first parameter is the user of the client. The
+second parameter is the new host the client is using.
+
+On irc daemons with support for changing the user portion of a client, the
+second form may appear:
+
+    :nick!user@host CHGHOST newuser host
+
+If specified, a client may also have their user and host changed at the same
+time:
+
+    :nick!user@host CHGHOST newuser new.host.goes.here
+
+This second and third form should only be seen on IRC daemons that support
+changing the user field of a user.
+
+In order to take full advantage of the CHGHOST message, clients must be modified
+to support it. The proper way to do so is this:
+
+1. Enable the chghost capability at capability negotiation time during the
+   login handshake.
+
+2. Update the user and host portions of data structures and process channel
+   users as appropriate.
+
+## Examples
+
+In this example, `tim!~toolshed@backyard` gets their username changed to `b` and
+their hostname changed to `ckyard`:
+
+    :tim!~toolshed@backyard CHGHOST b ckyard
+
+In this example, `tim!b@ckyard` gets their username changed to `~toolshed` and
+their hostname changed to `backyard`:
+
+    :tim!b@ckyard CHGHOST ~toolshed backyard
+
+## Errata
+
+A previous version of this specification did not include any examples, which made
+it unclear as to whether the de-facto `~` prefix should be included on CHGHOST
+messages. The new examples make clear that it should be included.
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