YUI is a free, open source JavaScript and CSS framework for building richly interactive web applications. YUI is provided under a BSD license and is available on GitHub for forking and contribution.

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This is the active working source tree for YUI 3. It contains work in progress toward the next YUI 3 releases and may be unstable.

We encourage you to use the latest source for evaluation purposes, testing new features and bug fixes, and to provide feedback on new functionality. Please refer to the "Latest Production Release" link above if you're looking for the latest stable release of YUI recommended for production use.

YUI's development happens on three main branches. The following describes what each of these code branches represents:

• live-docs: Represents the latest release of YUI, plus any documentation-only updates. Any tweaks or additions to the docs for the latest release happen on this branch, and they are reflected on the website.

• master: Contains everything in live-docs, plus code changes that will go into the next YUI release. The code changes in master are either bug fixes or small changes which should not break API compatibility. Patch releases will be cut from this branch; e.g. 3.6.x.

• 3.x: Represents the next major YUI release; e.g. 3.7.0. This is an integration branch which contains everything in master, plus larger code changes which will go into a future YUI release. The changes in 3.x require a minor version increment before they are part of release; e.g. 3.7.0. Preview Releases will be cut from this branch for developers to test and evaluate.

The YUI source tree includes the following directories:

• build: Built YUI source files. The built files are generated at development time from the contents of the src directory. The build step generates debug files (unminified and with full comments and logging), raw files (unminified, but without debug logging), and minified files (suitable for production deployment and use).

• src Raw unbuilt source code (JavaScript, CSS, image assets, ActionScript files, etc.) for the library. Beginning with YUI 3.4.0, the src directory also contains all module-specific documentation, tests and examples. All modifications to the library and its documentation should take place in this directory.

The individual component directories under the src directory contain Ant build files (build.xml and others) which can be used to build individual modules using the YUI Builder. The YUI Builder is part of the "builder" project, also available on GitHub at https://github.com/yui/builder

The README file in the componentbuild directory of the Builder project covers the installation and use of the build tool.