HTML 101

Introduction

HTML (HyperText Markup Language) is a markup language that tells web browsers how to structure the web pages you visit. It can be as complicated or as simple as the web developer wants it to be. HTML consists of a series of elements, which you use to enclose, wrap, or mark up different parts of content to make it appear or act in a certain way. The enclosing tags can make content into a hyperlink to connect to another page, italicize words, and so on. For example, consider the following line of text:

My cat is very grumpy

If we wanted the text to stand by itself, we could specify that it is a paragraph by enclosing it in a paragraph  element:

My cat is very grumpy

Tags in HTML are not case-sensitive. This means they can be written in uppercase or lowercase.

Prerequisites

One should have a basic knowledge of:

Computer syntax
Software installation
Working with computer files

One should have access to:

Computer with Internet access
Code text editor
Patience

Elements

Let's further explore our paragraph element from the previous section:

The anatomy of our element is:

The opening tag: This consists of the name of the element (in this example, p for paragraph), wrapped in opening and closing angle brackets. This opening tag marks where the element begins or starts to take effect. In this example, it precedes the start of the paragraph text.
The content: This is the content of the element. In this example, it is the paragraph text.
The closing tag: This is the same as the opening tag, except that it includes a forward slash before the element name. This marks where the element ends. Failing to include a closing tag is a common beginner error that can produce peculiar results.

The element is the opening tag, followed by content, followed by the closing tag.

Nesting Elements

Elements can be placed within other elements. This is called nesting. If we wanted to state that our cat is very grumpy, we could wrap the word "very" in a  element, which means that the word is to have strong(er) text formatting:

My cat is very grumpy.

There is a right and wrong way to do nesting. In the example above, we opened the p element first, then opened the strong element. For proper nesting, we should close the strong element first, before closing the p.

Block versus inline elements

There are two important categories of elements to know in HTML: block-level elements and inline elements.

Block-level elements form a visible block on a page. A block-level element appears on a new line following the content that precedes it. Any content that follows a block-level element also appears on a new line. Block-level elements are usually structural elements on the page. For example, a block-level element might represent headings, paragraphs, lists, navigation menus, or footers. A block-level element wouldn't be nested inside an inline element, but it might be nested inside another block-level element.
Inline elements are contained within block-level elements, and surround only small parts of the document's content (not entire paragraphs or groupings of content). An inline element will not cause a new line to appear in the document.

Attributes

Elements can also have attributes. Attributes look like this:

Attributes contain extra information about the element that won't appear in the content. In this example, the class attribute is an identifying name used to target the element with style information.

An attribute should have:

A space between it and the element name. (For an element with more than one attribute, the attributes should be separated by spaces too.)
The attribute name, followed by an equal sign.
An attribute value, wrapped with opening and closing quote marks.

Boolean attributes

Sometimes you will see attributes written without values. This is entirely acceptable. These are called Boolean attributes. Boolean attributes can only have one value, which is generally the same as the attribute name.

Documents

Individual HTML elements aren't very useful on their own. Next, let's examine how individual elements combine to form an entire HTML page:

<!DOCTYPE html>

            <html lang="en-US">

            <head>

            <meta charset="utf-8" />

            <title>My test page</title>

            </head>

            <body>

            <p>This is my page</p>

            </body>

            </html>

Here we have:

<!DOCTYPE html>: The document type. When HTML was young (1991-1992), doctypes were meant to act as links to a set of rules that the HTML page had to follow to be considered good HTML. More recently, the doctype is a historical artifact that needs to be included for everything else to work right.
<html>: This element wraps all the content on the page. It is sometimes known as the root element.
<head>: This element acts as a container for everything you want to include on the HTML page, that isn't the content the page will show to viewers. This includes keywords and a page description that would appear in search results, CSS to style content, character set declarations, and more.
<meta charset="utf-8">: This element represents metadata that cannot be represented by other HTML meta-related elements. Also sets the character set for your document to UTF-8, which includes most characters from the vast majority of human written languages. With this setting, the page can now handle any textual content it might contain. There is no reason not to set this, and it can help avoid some problems later.
<title>: This sets the title of the page, which is the title that appears in the browser tab the page is loaded in. The page title is also used to describe the page when it is bookmarked.
<body>: This contains all the content that displays on the page, including text, images, videos, games, playable audio tracks, or whatever else.

Whitespace in HTML

No matter how much whitespace you use inside HTML element content (which can include one or more space character, but also line breaks), the HTML parser reduces each sequence of whitespace to a single space when rendering the code. So why use so much whitespace? The answer is readability.

It can be easier to understand what is going on in your code if you have it nicely formatted. In our HTML we've got each nested element indented by two spaces more than the one it is sitting inside. It is up to you to choose the style of formatting (how many spaces for each level of indentation, for example), but you should consider formatting it.

Special Characters

In HTML, the characters <, >," ,' and & are special characters. They are parts of the HTML syntax itself. So how do you include one of these special characters in your text? For example, if you want to use an ampersand or less-than sign, and not have it interpreted as code.

You do this with character references. These are special codes that represent characters, to be used in these exact circumstances. Each character reference starts with an ampersand (&), and ends with a semicolon (;).

The character reference equivalent could be easily remembered because the text it uses can be seen as less than for '<', quotation for '" ' and similarly for others.

Comments

HTML has a mechanism to write comments in the code. Browsers ignore comments, effectively making comments invisible to the user. The purpose of comments is to allow you to include notes in the code to explain your logic or coding. This is very useful if you return to a code base after being away for long enough that you don't completely remember it. Likewise, comments are invaluable as different people are making changes and updates.

To write an HTML comment, wrap it in the special markers .

Summary

At this point, you should understand what HTML looks like, and how it works at a basic level. You should also be able to write a few elements and attributes. The subsequent articles of this module go further on some of the topics introduced here, as well as presenting other concepts of the language.