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== Changeset Library
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The https://github.com/ether/etherpad-lite/blob/develop/src/static/js/Changeset.js[changeset
library]
provides tools to create, read, and apply changesets.
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=== Changeset
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[source,javascript]
----
const Changeset = require('ep_etherpad-lite/static/js/Changeset');
----
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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).
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A transmitted changeset looks like this:
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[source]
----
'Z:z>1|2=m=b*0|1+1$\n'
----
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=== Attribute Pool
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[source,javascript]
----
const AttributePool = require('ep_etherpad-lite/static/js/AttributePool');
----
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Changesets do not include any attribute keyvalue pairs. Instead, they use
numeric identifiers that reference attributes kept in an https://github.com/ether/etherpad-lite/blob/develop/src/static/js/AttributePool.js[attribute pool].
This attribute interning reduces the transmission overhead of attributes that
are used many times.
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There is one attribute pool per pad, and it includes every current and
historical attribute used in the pad.
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=== Further Reading
Detailed information about the changesets & Easysync protocol:
* https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-notes.pdf[Easysync Protocol]
* https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-full-description.pdf[Etherpad and EasySync Technical Manual]