Introduction

Abstract
This is the 5th major revision of the core language of the World Wide Web. The HyperText Markup Language (HTML) a very popular and is in high demand. It's not just a newer version of HTML, it's a Web platform for techies that not only includes some new tags but also easy to extract data from web pages and delivers the content over multiple platforms and in multiple formats.
History
March 7, 2007, is the day when a new HTML Working Group (HTML WG, including representatives from Opera, Mozilla, and Apple) began working work on HTML in an open participation process and using hundreds of participants the next version of Web Applications 1.0 spec was adopted that is called HTML5.
As you might know, HTML 4 is the most successful markup format ever and all the success of HTML5 is based on HTML4 as all the controls of HTML 4 are supported by HTML5 and includes new input controls.
HTML5 Features
HTML5 APIs
After HTML's evolution later on in 1998 parts of the API for HTML developed by browser vendors and release as named DOM Level 1 then DOM Level 2 Core and after DOM Level 2 HTML and finally DOM Level 3.
Note: One thing you need to ensure is that HTML is not only used to write code as tags and angle brackets. The HTML5 specification also defines how JavaScript is interacting with those angle brackets using the Document Object Model (DOM). There is a DOM API for each corresponding tag.
Web browsers or you can say HTML user agents, parse your written markup into a DOM tree that represent the specific document in memory, each DOM tree contains several kinds of nodes, in particular, a DOCTYPE node, elements, etc.
Let's use an example of an HTML markup snippet and understand the DOM concept.
HTML markup snippet
  1. <!DOCTYPE HTML>
  2. <html>
  3. <head>
  4. <title>Your Page Title</title>
  5. </head>
  6. <body>
  7. <h1>Text</h1>
  8. <p>Text</p>
  9. <!-- Comment -->
  10. </body>
  11. </html>
DOM tree of HTML markup snippet
To enhance the interactivity of your pages HTML5 also offers several JavaScript APIs, Some HTML5 APIs are still fairly new, and not every version of every browser supports them but HTML5 is a collection of individual features. So you can't define HTML5 support (like this browser can't support HTML5), you can detect support for individual features, like canvas, video, or geolocation.
First, understand what an API is. An API (Application Programming Interface) is a collection of programming instructions and standards for accessing a software application and by using any API, you design a product supported by the service the API provides.
By using HTML5 APIs you are able to include most advanced features and interaction that provides really interesting features to your web page.
In HTML5 you can use many APIs. Some of them are:
The following is only a brief introduction to each API and in detail, I will explain each one of them in my future articles in this series of Learning HTML5.
Checking Browser Compatibility
It is always good to check the browser compatibility before working on HTML5 APIs whether or not the feature is supported by your browser. Before using any API, refer to a compatibility chart that shows which browsers support that API.
I Personally use caniuse.com to check the HTML5 APIs compatibility. For example, see in the following image I am searching for the compatibility of Web Workers:
You can also check for browser compatibility of API features in your JavaScript code.
The following example shows how to check the support for Web Workers
  1. if (!!window.Worker) {
  2. //do something
  3. }
  4. else {
  5. //do something
  6. }

Summary

And so this is the introduction to the HTML5 APIs. I hope it's useful for you, and that you continue reading the future articles about HTML5 referenced above.