Differences between HTML 4.01 and HTML5

Some of the differences, so far, are to be expected.

Structuring elements:

article
The article includes an independent element section, which is, however, in the context of the ancestor elements. This applies to, for example, news articles, blogs or forum entries.

aside
This element identifies content that fits the theme surrounding the content but is not directly entailed by it. A policy might contain a message body aside element that cross-references to similar messages.

Dialog
An element is specially imported for dialogue.

figure
The figure element allows a particular medium (e.g., images, videos, etc.) to bear a caption.

footer
The footer element defines a footer for the current section (for example, in an article-element) there is, for example, information about the author or the creation time of the text.

header
The header element defines the header for the current section (for example) in a section element. In addition to a headline, it can have further necessary information, such as version information.

nav
This element encloses a navigation area. This not only links to other pages with a web presence here, but, for example, allows the references to sections within a document to show (as in Wikipedia).

section
A section element groups thematically related content, and usually has a header and footer. Based on a typical Web page, examples of a section-element would, as one might imagine, a message and a contact area.

Elements for data representation:

audio, video
Audio and video files are to be included in the future with these elements. HTML5 provides some interfaces to these elements, such as being able to control playback.
embed
With the embed element, applications and interactive content can be added. The element is the standardization of a previously proprietary element.

mark
The mark element is highlighted text. This is not to be confused with underlined text. Instead, it visibly marks the text that was found by a search engine, enabling users to quickly find their presentation programs.
meter
The meter element represents a share compared to its maximum. Using this item one can view, for example, how good the result is compared to the search term, i.e., how well a product compares to the highest rating, cuts, etc.

source
This item allows for a media element in a variety of given sources, from which the display program selects the appropriate one.

time
The time element is used to indicate dates and times.  It is equipped with metadata so that a browser can generate, for example, an interactive calendar.

Application elements:

canvas
The canvas element to create a drawing surface that can be drawn with the help of DOM methods. The specification provides only a two-dimensional drawing surface, but it is expected that three-dimensional contexts could be introduced in the future.

progress
The progress element reflects the progress of a particular task. The element is also controlled with the DOM. An example is the progress of a multi-page survey.

Forms
Also, some new forms have been defined. Originally they were developed in a separate specification called Web Forms 2.0. Since its inclusion in the separate development of HTML5, Web Forms 2.0 has been discontinued. This specification is already very mature and brings new features such as these:
New input types, such as e-mail addresses, Internet addresses, dates, etc., so that the browser can check them for syntactic correctness.
Input fields can be defined as a mandatory field.
Input templates can be created and can be added dynamically (for example, to an order form) to expand the possible entries.
Data lists, for example, to generate an adjustable control object, such as the volume of an audio or video element.
Clarify how CSS properties affect the form elements.

Mapped elements
Some elements have been redefined to suit their application:

i
Previously, this element produced italic text. Now it identifies text that are usually written in italics, such as text in a different voice or mood, thoughts, etc.
b
Previously, the b element formatted text in bold. Now the text that should be identified is text that should be emphasized, although only stylistically, as it has no more important significance than the rest of the text, e.g., keywords, product names, etc.

em
This item still distinguishes text that should be emphasized. The emphasis is now enhanced, however, if this element is nested.
hr
This was the first generation of a dividing line. Now, this dividing line symbolizes a thematic break between paragraphs.
small
In the past, this formatted text smaller than normal. Now, fine print is to reserved, for example, for genuine author references, disadvantages by asterisk correlation, and legal restrictions.

strong
Earlier this award meant a strong emphasis. This is now being taken by em-nested elements. The strong element now distinguishes great importance.

Once enabled elements
The attribute start of the ol element and the value attribute of the li element is once again part of the core language.

New DOM methods
Additional methods were added for controlling audio and video elements, as was a method called getElementsByClassName. This method puts together all the elements of a particular class within a document (for more class information at the same time is possible). Javascript has now implemented this functionality, but a version implemented in the browser would handle the task quickly and efficiently.
Distant elements and attributes
The following elements have been removed:

acronym
Instead, only the abbr element for abbreviations should be used because it is more general, and the acronym element alone may also reflect the versatile little acronyms.

Big & tt are also elements that have been removed.

Also, some attributes have been removed. Stark was criticized in this regard; however the absence of the attributes of the summary header element and axis should make the tables more accessible. Since the specification is still a draft, it is unclear whether these attributes will or will not be added. In XHTML5 (MIME type application / xhtml + xml), the noscript element is no longer allowed because the element model is compatible with the XML processing rules. Text in HTML5 (Mime-Type text / html) is allowed to continue noscript.