The lead up to the official debut of HTML 5 in October 2014 was a very big deal. Now two years later HTML 5.1 was declared an official standard on November 1.
With HTML 5 work was ongoing for more than seven years and the standard replaced HTML 4.x which had been in place for a decade. HTML 5.1 in contrast is a very incremental step up, dealing with minor items that fell out from the original HTML 5 approach.
The features that HTML 5.1 add are:
• The picture and srcset attributes allow responsive image selection.
• The details andsummary elements enable authors to provide extended information that users can choose whether to read.
• The menuitem and type="context" attribute value enable authors to add functionality to the browser’s context menu.
• The requestAnimationFrame API allows for more efficient animation.
• enqueueJob and nextJob help explain Promise resolution in terms of microtasks.
• The rev attribute for links, primarily to support RDFa (previously defined in HTML 4).
• HTMLMediaElement and srcObject objects.
• Enable cross-origin track and EventSource and cross-origin content for ImageBitmap in canvas.
• event-source-error, event-track-error and event-track-load events for media fetching.
• onrejectionhandled and onunhandledrejection and APIs for tracking promise rejection.
• HTMLTableCaptionElement, HTMLTableSectionElement, HTMLTableRowElement, for HTML table elements.
• history.scrollRestoration to control where a users' view is directed when navigating through their history.
• IDL [SameObject], for some objects that return collections.
• Add "noopener" to rel and window to allow for browsing contexts to be separated.
• nonce attribute on script and style to support the use of Content Security Policy.
A few interesting things, but nothing really groundbreaking and nothing that will actually impact the end-user experience today either. As was the case with the debut of HTML 5, browser vendors have long since moved waiting for the W3C before using new web technologies.
The big push now from the web vendors is in support of native code, things like 'C' in the browser, which has been talked about for many years, but has never been implemented in a truly standardized way.