Contributor-license-agreement-etc.md

+MathJax is licensed under the [Apache License 2.0](https://github.com/mathjax/MathJax/blob/master/LICENSE). 
+
+Due to the modular structure of MathJax, contributions can come in two distinct forms: modifications of the core code (i.e., the code under the copyright of the MathJax consortium) as well as extensions, translations and other additions that can be removed easily.
+
+Contributions of the second kind do not require a contributor license agreement (CLA) or copyright assignment agreement (CAA). Such contributions only require the [Apache License 2.0](https://github.com/mathjax/MathJax/blob/master/LICENSE). Because of Section 5 of the [Apache License 2.0](https://github.com/mathjax/MathJax/blob/master/LICENSE)), the contributor’s active decision to submit code to the MathJax project should be sufficient.
+
+If you want to contribute to the core of MathJax, please contact us.
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