The very first draft HTML spec, https://www.w3.org/MarkUp/draft-ietf-iiir-html-01.txt (June 1993), is somewhat interesting here, because the only element with optional start and end tags is the html element (head and body require both start and end tags, per that spec).
Certainly by the point of HTML 2.0 (November 1995; the first non-draft spec for HTML) all three elements have start and end tags all optional.
The more general ability to omit start/end tags from given elements is a feature of SGML (October 1986), and HTML 2.0 to HTML 4.01 were defined as SGML applications (though approximately nothing ever used an SGML parser for HTML).
Chrome uses its own Blink and V8 now, and there are many cases where developers only design for Chrome and small differences in implementation can be a huge pain in Firefox/Safari.
No professional developer targets a browser when developing a web site unless its a captured audience with no choice. Professional developers follow the specification. Those who do otherwise are only mentioned in reddit headlines and other hobbyist sites.
You're missing my point. Assuming that all browsers correctly implement the specification is naive. I don't have an issues with standards themselves existing.
They are implied. I believe this dates back to when browsers supported non-standard HTML and the behavior of doing it was cemented in HTML5 (like tag soup and so forth.) Since it was based on existing behavior it should work even in old IE, just like the doctype.
