Code Guide is a project created by Mark Otto (one of the Bootstrap Framework creators) for documenting standards for developing flexible, durable, and sustainable HTML and CSS. It comes from his years of experience writing code on projects of all sizes. It's not the end-all be-all, but it's a start.
Licence: Released under MIT by, and copyright 2014, @mdo.
Translations: Portuguese, Spanish, Indonesian, Chinese, Italian, Russian, Czech and Traditional Chinese.