The (SDN) Microsoft Development Network Library Select Web Development in the table on the left of the page.
Home page of the World Wide Web Consortium Standards are called Recommendations. They can be extremely wordy, but all the details are specified. Most vendors do not violate the standards much, but most leave a lot unimplemented. For HTML, see HTML 4.01. For CSS, see CSS 2.1.
The ECMAScript language specification This is not a text. Use it for reference.
W3 Schools W3 Schools: a wealth of information, examples, and tutorials