# Codebase Overview

## Overview of Comm Central

The following directories are included in the comm-central repository:

**build**\
Miscellaneous files used by the build process.

**calendar**\
The calendar component of Thunderbird (formerly known as the Lightning extension).

[**chat**](/thunderbird-development/codebase-overview/chat.md)\
Files for the chat component of Thunderbird. There is also related code in `mail/components/im`.

The subdirectories are:

* **components** Various chat features, includes the interfaces that each protocol must implement.
* **content** User interface files which become `chrome://chat/content/…`.
* **locales** The user-visible strings, in US English. Files from this directory become `chrome://chat/locale/…`.
* **modules** JavaScript modules that are specific to chat.
* **protocols** Various protocol implementations. Each of subdirectory implements a protocol to the interfaces found under **components**.
* **themes** Common and platform-specific styling specific to chat. Files from this directory become `chrome://chat/skin/…`.

**mail**\
Thunderbird specific source code. It's no coincidence that this folder is laid out a lot like the `browser` and `toolkit` directories on mozilla-central. Many of the subdirectories follow the same pattern:

* **content** User interface files which become `chrome://messenger/content/…`.
* **modules** Javascript modules which become `resource:///modules/…`.
* **test** Mochitest and/or XPCShell tests.

The subdirectories are:

* **actors** Modules which handle communication between processes. [See the Firefox documentation for information about actors](https://firefox-source-docs.mozilla.org/dom/ipc/jsactors.html).
* **app** Configuration and packaging instructions. Contains `all-thunderbird.js`, the default preferences.
* **base** The main mail window and several miscellaneous dialogs. Also, things which are common to many parts of the program.
* **branding** Icons and imagery.
* **components** Various Thunderbird features, including:
  * **accountcreation** The account setup wizard.
  * **addrbook** The address book user front end. (Not the address book back end, which is in `mailnews/addrbook`).
  * **cloudfile** The cloud attachment feature (a.k.a. FileLink).
  * **compose** Email composition window.
  * **extensions** WebExtensions schema and implementation.
  * **im** The chat front end.
  * **preferences** The preferences tab.
* **config** Build instructions, including the automation mozconfig files.
* **extensions**
* **installer** Packaging and installation instructions.
* **locales** The user-visible strings, in US English. Files from this directory become `chrome://messenger/locale/…`.
* **modules** Shared JS modules. Files from this directory become `resource:///modules/….`
* **test** The MozMill user interface tests and the code to run that test suite.
* **themes** Common and platform-specific styling of Thunderbird user interface. Files from this directory become `chrome://messenger/skin/…`.

**mailnews**\
Source code specific to the Mail and Newsgroups part of Thunderbird and SeaMonkey.

**mozharness**\
Files needed for Thunderbird's test infrastructure.

**other-licenses**\
Code that is not under the Mozilla license. See <http://www.mozilla.org/MPL/> for more info.

**suite**\
SeaMonkey-specific source code. Not used in Thunderbird.

**taskcluster**\
Files needed for Thunderbird's build infrastructure.

**testing**\
Files needed for Thunderbird's test infrastructure.

**third\_party**\
Libraries developed elsewhere that are included in Thunderbird


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