Added vitepress for documentation. (#6270)

doc/api/changeset_library.md

@@ -0,0 +1,44 @@
+# Changeset Library
+
+The [changeset
+library](https://github.com/ether/etherpad-lite/blob/develop/src/static/js/Changeset.js)
+provides tools to create, read, and apply changesets.
+
+## Changeset
+
+```javascript
+const Changeset = require('ep_etherpad-lite/static/js/Changeset');
+```
+
+A changeset describes the difference between two revisions of a document. When a
+user edits a pad, the browser generates and sends a changeset to the server,
+which relays it to the other users and saves a copy (so that every past revision
+is accessible).
+
+A transmitted changeset looks like this:
+
+```
+'Z:z>1|2=m=b*0|1+1$\n'
+```
+
+## Attribute Pool
+
+```javascript
+const AttributePool = require('ep_etherpad-lite/static/js/AttributePool');
+```
+
+Changesets do not include any attribute key–value pairs. Instead, they use
+numeric identifiers that reference attributes kept in an [attribute
+pool](https://github.com/ether/etherpad-lite/blob/develop/src/static/js/AttributePool.js).
+This attribute interning reduces the transmission overhead of attributes that
+are used many times.
+
+There is one attribute pool per pad, and it includes every current and
+historical attribute used in the pad.
+
+## Further Reading
+
+Detailed information about the changesets & Easysync protocol:
+
+* [Easysync Protocol](https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-notes.pdf)
+* [Etherpad and EasySync Technical Manual](https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-full-description.pdf)