How does an HTML specification differ from a web browser's implementation of the same?

Question

The main function of a browser is to present the web resource you choose, by requesting it from the server and displaying it in the browser window. The way the browser interprets and displays HTML files is specified in the HTML and CSS specifications. The two biggest differences between web browsers are support and rendering. Which is the cause of differing from a web browser's implementation or something else?

Answer 1

No specification is 100% clear and it sometimes gives multiple ways to interpret things. Also there could be irregularities due to the way many things are implemented. This also is the case for the ECMAScript standard.