Phase 1 of 7

Lesson Introduction

Have you ever visited a website and seen strange symbols like â€™ or Ã© instead of normal text? Or copied a URL from a browser and seen something like https://example.com/search?q=hello%20world? Or wondered why your browser sometimes shows broken characters when a page contains non-English text?

All of these mysteries come down to three closely connected topics that every web developer must understand:

Character Sets (Charsets) · how computers agree on which patterns of bits represent which letters and symbols
URL Encoding · how web addresses safely carry special characters across the internet
XHTML · a stricter version of HTML that follows XML rules, and what it teaches us about writing clean, correct HTML

By the end of this lesson, you will be able to:

Explain what a character set is and why UTF-8 is the global standard
Correctly declare a character set in any HTML page
Read and decode URL-encoded strings
Understand the full anatomy of a web address (URL)
Explain the key differences between HTML and XHTML
Write HTML that meets XHTML's stricter standards · making your code cleaner and more reliable

Real-World Connection: When you build a website that must display Yoruba, Arabic, Chinese, or French characters alongside English · or when you build a search form whose data travels safely through URLs · these three topics are exactly what you need.

✏️ Your Task

Practise what you just learned about Lesson Introduction. Open your editor, type the examples above by hand, modify them, and observe what changes.

Phase 2 of 7

Prerequisite Concepts

Before diving in, let's make sure three foundational ideas are clear.

What is a Bit and a Byte?

A bit is the smallest unit of data in a computer. It can only be a 0 or a 1. Think of it like a light switch · either OFF (0) or ON (1).

A byte is a group of 8 bits. With 8 switches, each either on or off, you can make 2⁸ = 256 different combinations.

code

00000000 = 0
00000001 = 1
00000010 = 2
01000001 = 65
11111111 = 255

What is a Character?

A character is any single letter, digit, punctuation mark, or symbol that you can type or display. For example: A, z, 3, @, £, é, ₦, 中.

What is Encoding?

Encoding is a system of rules that assigns a number to each character. The computer stores that number in binary (as bits), and when you read it back, the rules decode the number back into the right character.

Without agreed-upon encoding rules, one computer sending a letter A might look like £ on another computer · complete garbled nonsense.

✏️ Your Task

Practise what you just learned about Prerequisite Concepts. Open your editor, type the examples above by hand, modify them, and observe what changes.

Phase 3 of 7

Part 1: HTML Character Sets (Charsets)

1.1 · Why Browsers Need to Know the Character Set

When a browser receives an HTML file from a server, it sees a stream of raw bytes · just numbers. Those bytes represent text, but the browser cannot display the correct characters unless it knows which encoding was used to write that file.

This is like receiving a secret message in code. Before you can read it, you need to know which cipher (code system) was used.

The <meta charset="..."> tag in the <head> section of your HTML page tells the browser which encoding to use to decode the file.

The standard way to declare a character set in HTML5:

html

<meta charset="UTF-8">

This one line, placed inside <head>, is all you need. The browser will then correctly decode and display all characters in the file using the UTF-8 rules.

Important: The HTML specification strongly encourages all web developers to use UTF-8. It is the recommended character set for all modern webpages.

1.2 · The History of Character Sets: From ASCII to UTF-8

Character encoding systems have evolved over decades. Understanding this history helps you understand why we use UTF-8 today.

Stage 1: ASCII · The Original Internet Character Set

ASCII stands for American Standard Code for Information Interchange.

ASCII was the first character encoding standard used on the web. It defined 128 different characters · enough for the English language and basic symbols.

Here is what ASCII covers:

English letters: a to z and A to Z
Digits: 0 to 9
Common symbols: ! $ + - ( ) @ < > . # ?

ASCII uses numbers 0 to 127. Each character is stored as a number in that range.

ASCII number examples:

Character	ASCII Number	Binary
A	65	01000001
B	66	01000010
a	97	01100001
0	48	00110000
Space	32	00100000

Simple Example · What ASCII "sees":

If you type the word Hi in ASCII, the computer stores it as:

code

H = 72 = 01001000
i = 105 = 01101001

The file actually contains these two byte values. When the browser reads them back and uses ASCII rules, it displays Hi.

The Problem with ASCII: ASCII only covers 128 characters · great for English, but the world has thousands of other scripts: Arabic, Chinese, Yoruba, Greek, Hebrew, Hindi, Japanese, and many more. ASCII has no way to represent any of them.

Stage 2: ANSI (Windows-1252)

ANSI · also called Windows-1252 · was the character set used by Windows operating systems.

Key facts about ANSI:

Characters 0 · 127 are identical to ASCII (same numbers, same letters)
Characters 128 · 159 are special symbols specific to ANSI (e.g., €, Ž, ™)
Characters 160 · 255 are the same as UTF-8 in that range

To use ANSI in HTML5, you would write:

html

<meta charset="Windows-1252">

Why ANSI is no longer recommended: ANSI was designed for Western European languages. It still does not support Arabic, Chinese, or most African language scripts. It was a step forward from ASCII but still far too limited for the global web.

Stage 3: ISO-8859-1 · The Default for HTML 4

ISO-8859-1 (also called Latin-1) was the default character set for HTML version 4 (the version before HTML5).

Key facts about ISO-8859-1:

Characters 0 · 127 are identical to ASCII
Characters 128 · 159 are NOT used (left empty)
Characters 160 · 255 are the same as ANSI and UTF-8 in that range

It supported 256 characters total · covering Western European languages like French, Spanish, German, and Portuguese.

How to declare ISO-8859-1:

In HTML 4 (old style):

html

<meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">

In HTML5 (simpler):

html

<meta charset="ISO-8859-1">

Why ISO-8859-1 is no longer used: Like ANSI, 256 characters is nowhere near enough for the world's writing systems. Modern HTML5 pages should always use UTF-8.

Stage 4: UTF-8 · The Universal Standard

UTF-8 stands for Unicode Transformation Format · 8-bit.

UTF-8 is the modern, universal character encoding used by virtually all websites today. Here is what makes it special:

Characters 0 · 127 are identical to ASCII · so all basic English text works perfectly
Characters 128 · 159 are NOT used (for safety)
Characters 160 · 255 are the same as ANSI and ISO-8859-1
Characters 256 and beyond extend to over 1,000,000 characters · covering every writing system on Earth

What UTF-8 can display:

All English letters and numbers ✓
Western European accented letters (é, ñ, ü, ô) ✓
African scripts (Yoruba: ẹ, ọ, ṣ) ✓
Arabic (مرحبا) ✓
Chinese (你好) ✓
Japanese (こんにちは) ✓
Hindi (नमस्ते) ✓
Emojis (😊 🌍 🎉) ✓
Mathematical symbols (∑ ∞ √) ✓
Currency symbols (£ € ¥ ₦ ₹) ✓

How to declare UTF-8 (the modern, correct way):

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>My UTF-8 Page</title>
</head>
<body>
  <p>Hello World!</p>
  <p>Bonjour le monde!</p>
  <p>Olá Mundo!</p>
  <p>مرحبا بالعالم</p>
  <p>你好世界</p>
</body>
</html>

Expected Output in browser:

code

Hello World!
Bonjour le monde!
Olá Mundo!
مرحبا بالعالم
你好世界

All five lines display correctly because UTF-8 knows how to decode every character.

Thinking Prompt: What do you think would happen if the page used charset="ISO-8859-1" instead of charset="UTF-8", but the file actually contained Chinese characters? The browser would try to decode the Chinese bytes using ISO-8859-1 rules and display completely wrong symbols · the classic "mojibake" (garbled text) problem.

1.3 · The Unicode System and UTF-8

Unicode is an international standard that assigns a unique number (called a code point) to every character from every writing system in the world.

Think of Unicode as a universal dictionary: every character in every language has a unique ID number.

For example:

A is Unicode code point U+0041
é is Unicode code point U+00E9
中 is Unicode code point U+4E2D
₦ (Naira symbol) is Unicode code point U+20A6
😊 is Unicode code point U+1F60A

UTF-8 is the most popular way of storing Unicode code points in bytes. It is efficient: common characters (like English letters) use just 1 byte, while rarer characters use 2, 3, or 4 bytes.

1.4 · Character Set Quick Reference Table

Character Set	Year Popular	Characters Covered	Recommended?
ASCII	1960s · 1990s	128 (English + basic symbols)	No · too limited
ANSI (Windows-1252)	1990s · 2000s	256 (Western Europe + English)	No · legacy only
ISO-8859-1	1990s · 2000s	256 (Western Europe + English)	No · HTML 4 era
UTF-8	2000s · now	1,000,000+ (all world languages)	YES · always use this

1.5 · A Sample of UTF-8 Character Groups

UTF-8 can represent an enormous variety of scripts. Here are some of the character groups available:

Basic Latin · ABCD abcd 0123 ?#$% (same as ASCII)
Latin Extended A · ĀĂĄ ĆĈĊ ĒĔĖĘ (extra letters for European languages)
Latin Extended B · ƀƁƂ ƆƇ ƉƊ (more phonetic and historic Latin)
Diacritical Marks · àáâã èéêẽ òóôõ (accent marks added to letters)
General Punctuation · ‰ ‱ ⁒ ‼ ⁇ ⁈ (advanced punctuation)
Super and Subscript · C⁰ Cⁱ C⁴ C₆ C₇ (for scientific notation)
Braille · ⠓⠑⠇⠇⠕ (for accessibility)
Hundreds more groups covering Arabic, Hebrew, Devanagari, CJK (Chinese/Japanese/Korean), African scripts, emoji, symbols, and more

1.6 · Where to Put the `charset` Declaration

The <meta charset="UTF-8"> tag must go inside the <head> section, and it should be one of the very first lines · ideally within the first 1,024 bytes of the file. This is because the browser begins decoding the file immediately, and it needs to know the character set before it encounters any non-ASCII characters.

Correct placement:

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">          <!-- ← Must be near the top of <head> -->
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Page Title</title>
</head>
<body>
  <!-- page content here -->
</body>
</html>

Common mistake · wrong placement:

html

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
  <!-- Other meta tags -->
  <meta charset="UTF-8">    <!-- ← Too late! Should come first in <head> -->
</head>

✏️ Your Task

Practise what you just learned about : HTML Character Sets (Charsets). Open your editor, type the examples above by hand, modify them, and observe what changes.

Phase 4 of 7

Part 2: URL Encoding

2.1 · What is a URL?

Before we can understand URL encoding, we need to understand what a URL is and how it is structured.

URL stands for Uniform Resource Locator. It is the technical name for a web address · the string you type into your browser to visit a website.

Examples of URLs:

code

https://www.google.com
https://www.w3schools.com/html/default.asp
ftp://files.example.com/documents/report.pdf
file:///C:/Users/Jane/Documents/index.html

2.2 · The Anatomy of a URL

Every URL is made up of several named parts. Let's break down this example:

code

https://www.w3schools.com/html/default.asp

The full URL syntax is:

code

scheme://prefix.domain:port/path/filename

Let's understand each part:

Part	Name	What it does	Example
`https`	Scheme	Defines the type of internet service	`http`, `https`, `ftp`, `file`
`www`	Prefix	Defines the domain prefix	`www` is the default for web pages
`w3schools.com`	Domain	The internet domain name (the website's address)	`google.com`, `bbc.co.uk`
(not shown)	Port	The port number at the host	Default for http is `80`, https is `443`
`/html/`	Path	A path (folder) at the server	`/html/`, `/images/`, `/blog/`
`default.asp`	Filename	The specific document or resource	`default.asp`, `index.html`

Let's break down a more complete URL:

code

https://www.bbc.co.uk:443/news/world/africa/article.html
  │        │    │       │    │          │
  │        │    │       │    │          └── filename: article.html
  │        │    │       │    └── path: /news/world/africa/
  │        │    │       └── port: 443
  │        │    └── domain: bbc.co.uk
  │        └── prefix: www
  └── scheme: https (secure)

Thinking Prompt: Why do you think websites use https:// instead of http://? The s stands for secure · the data is encrypted so no one can spy on what you send or receive.

2.3 · Common URL Schemes

A scheme tells the browser what type of service it is connecting to.

Scheme	Stands For	Used For
`http`	HyperText Transfer Protocol	Regular web pages · NOT encrypted
`https`	Secure HyperText Transfer Protocol	Secure web pages · encrypted
`ftp`	File Transfer Protocol	Uploading or downloading files
`file`	(none)	Opening a file stored on your local computer

Simple examples:

code

http://www.oldsite.com              ← Not encrypted (avoid for sensitive data)
https://www.bankwebsite.com         ← Encrypted (good for login, payments)
ftp://files.myserver.com/report.pdf ← File download via FTP
file:///C:/my-project/index.html    ← Local file on your computer

Real-World Note: Modern browsers show a padlock icon 🔒 for https:// pages and may warn users about http:// pages. Always use https:// for any site that handles personal data.

2.4 · Why URL Encoding Exists

Here is the key rule you must know:

URLs can only contain characters from the ASCII character set.

This means URLs cannot contain spaces, accented letters, symbols like £, or characters from non-English scripts like Arabic or Chinese · at least not directly.

But what if a user types a search query like hello world or café into a search box? Or what if a web address needs to contain a &, =, or ? in a path where those characters have special meaning?

The solution is URL Encoding: a system that converts any problematic character into a safe format that URLs can carry.

2.5 · How URL Encoding Works

URL encoding works by replacing unsafe characters with a percent sign % followed by two hexadecimal digits representing that character's value in UTF-8.

Key rule:

unsafe character → % + hex code

The most important example is the space character:

A space is encoded as %20 (or sometimes a + sign in form data)

Examples of URL encoding:

Character	URL Encoded Form	Explanation
Space	`%20` or `+`	Space is not allowed in URLs
`&`	`%26`	`&` has special meaning in URLs (separates parameters)
`=`	`%3D`	`=` has special meaning (assigns parameter values)
`#`	`%23`	`#` has special meaning (page anchors)
`+`	`%2B`	`+` is used for space, so literal `+` needs encoding
`/`	`%2F`	`/` separates URL path segments
`?`	`%3F`	`?` starts the query string
`@`	`%40`	`@` has special meaning in URLs
`£`	`%C2%A3`	Non-ASCII character (British Pound)
`©`	`%C2%A9`	Non-ASCII character (copyright symbol)
`€`	`%E2%82%AC`	Non-ASCII character (Euro sign)
`®`	`%C2%AE`	Non-ASCII character (registered trademark)

Notice: Non-ASCII characters like £, ©, € need multiple percent-encoded bytes because in UTF-8 they require more than one byte to represent.

2.6 · Real-Life URL Encoding Examples

Example 1 · A search query with spaces:

When you search for Lagos weather today on Google, your browser converts this to:

code

https://www.google.com/search?q=Lagos%20weather%20today

? · begins the query string
q= · the parameter name (query)
Lagos%20weather%20today · the search text, with spaces encoded as %20

Example 2 · A URL with special characters:

Searching for C++ programming:

code

https://www.example.com/search?q=C%2B%2B+programming

C%2B%2B · the + signs are encoded as %2B (because + itself means space in form data)
+programming · the space before "programming" is encoded as +

Example 3 · Multiple URL parameters:

A shopping website might build this URL when you filter products:

code

https://shop.example.com/products?category=books&price=1000&sort=newest

? · starts the query string
category=books · first parameter
& · separates parameters (this is why & itself needs to be encoded if it appears inside a value)
price=1000 · second parameter
&sort=newest · third parameter

2.7 · ASCII Encoding Examples by Character Set

The same character can be encoded differently depending on the character set being used. Here is a comparison between Windows-1252 (ANSI) and UTF-8 encodings for the same characters:

Character	Name	Windows-1252 Encoding	UTF-8 Encoding
`€`	Euro sign	`%80`	`%E2%82%AC`
`£`	Pound sign	`%A3`	`%C2%A3`
`©`	Copyright	`%A9`	`%C2%A9`
`®`	Registered mark	`%AE`	`%C2%AE`
`À`	A with grave	`%C0`	`%C3%80`
`Á`	A with acute	`%C1`	`%C3%81`
`Â`	A with circumflex	`%C2`	`%C3%82`
`Ä`	A with umlaut	`%C4`	`%C3%84`
`Å`	A with ring	`%C5`	`%C3%85`

Why are they different? Because Windows-1252 uses a single byte for each of these characters (fitting into the range 128 · 255), while UTF-8 needs two or three bytes for the same characters. Each byte gets its own %XX code. This is why the HTML5 specification defaults to UTF-8 · it ensures consistent encoding everywhere.

2.8 · How URL Encoding Appears in Practice

When you use an HTML form to send data, the browser automatically encodes the input before sending it. You don't need to encode manually in most cases · but you do need to understand what is happening.

Example · A simple search form:

html

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Search Example</title>
</head>
<body>

  <form action="/search" method="GET">
    <label for="query">Search:</label>
    <input type="text" id="query" name="q">
    <button type="submit">Search</button>
  </form>

</body>
</html>

What happens when user types "Lagos Festival 2026" and clicks Search:

The browser automatically URL-encodes the input and navigates to:

code

/search?q=Lagos+Festival+2026

or equivalently:

code

/search?q=Lagos%20Festival%202026

The spaces become either + or %20 · both are valid. The server receives the value and decodes it back to Lagos Festival 2026.

Thinking Prompt: What URL would the browser generate if the user typed naira ₦ exchange rate? The ₦ (Naira symbol) is not ASCII, so it would be encoded in UTF-8 bytes as %E2%82%A6.

✏️ Your Task

Practise what you just learned about : URL Encoding. Open your editor, type the examples above by hand, modify them, and observe what changes.

Phase 5 of 7

Part 3: HTML vs. XHTML

3.1 · What is XHTML?

XHTML stands for eXtensible HyperText Markup Language.

It is a version of HTML that was rewritten to follow the strict rules of XML (eXtensible Markup Language).

Think of it this way:

HTML is like a forgiving teacher · if you make small mistakes (like forgetting a closing tag), the browser will try its best to fix them and still show the page.
XHTML is like a strict examiner · if you make any mistake at all, the document is considered invalid and may not work.

3.2 · Why Was XHTML Created?

The Problem with "Forgiving" HTML:

Standard HTML browsers have always been very tolerant of mistakes. If you forget a closing tag, use uppercase tag names, or miss a quote on an attribute value, most browsers will still display the page. They have built-in error correction code to guess what you meant.

This sounds helpful, but it caused problems:

Developers got lazy and wrote sloppy code
Browsers had to implement complex (and sometimes inconsistent) error-fixing logic
Pages sometimes looked different in different browsers because each browser guessed differently
HTML pages could not easily be processed by other software that expected clean, well-formed data

The XHTML Solution:

XML is a stricter data format used across the web for data exchange. XHTML applied XML's strict rules to HTML:

All tags must be properly nested
All tags must be closed
All attributes must be quoted
Tag and attribute names must be lowercase

This made documents predictable, consistent, and processable by any XML tool.

3.3 · The Nine Key Differences: HTML vs. XHTML

Here are all the important rules that XHTML requires that standard HTML does not enforce:

Difference 1: `<!DOCTYPE>` is Mandatory in XHTML

In HTML5, the doctype is short and simple. In XHTML, a longer, specific DOCTYPE declaration is required.

XHTML DOCTYPE (required):

html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

HTML5 DOCTYPE (much simpler):

html

<!DOCTYPE html>

Difference 2: The `xmlns` Attribute in `<html>` is Mandatory

In XHTML, the <html> tag must include a special attribute called xmlns (XML Namespace) that declares this document follows XHTML rules.

XHTML <html> tag:

html

<html xmlns="http://www.w3.org/1999/xhtml">

HTML5 <html> tag:

html

<html lang="en">

Difference 3: `<html>`, `<head>`, `<title>`, and `<body>` are All Mandatory

In HTML5, technically some of these can be omitted (the browser implies them). In XHTML, all four must be present. A minimum valid XHTML document looks like this:

html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Title of document</title>
</head>
<body>
  <p>Some content here...</p>
</body>
</html>

Difference 4: Elements Must Always be Properly Nested

Nesting means opening and closing tags must be correctly matched · inner tags must close before outer tags close.

Correct (XHTML and good HTML):

html

<b><i>Bold and italic text</i></b>

The  tag opens inside , so  must close before  closes.

Wrong (invalid in XHTML, but browsers may fix it in HTML):

html

<b><i>Bold and italic text</b></i>

Here  closes before , which is incorrect overlapping.

Analogy: Think of nested tags like nested cups. If you put a small cup inside a large cup, you must take the small cup out first before you can move the large cup. Tags work the same way.

Difference 5: Elements Must Always be Closed

In HTML, some elements do not require a closing tag. Browsers assume where they end. In XHTML, every element must be explicitly closed.

HTML (lenient · this is allowed):

html

<p>This is a paragraph
<p>This is another paragraph

XHTML (strict · closing tags required):

html

<p>This is a paragraph</p>
<p>This is another paragraph</p>

Difference 6: Empty Elements Must Always be Closed

Empty elements are tags that have no content and no closing tag in HTML · for example  , <hr>, <img>. In XHTML, even empty elements must be closed using a self-closing slash.

Element	HTML (allowed)	XHTML (required)
Line break	`<br>`	`<br />`
Horizontal rule	`<hr>`	`<hr />`
Image	`<img src="x.jpg">`	`<img src="x.jpg" />`
Input	`<input type="text">`	`<input type="text" />`
Meta	`<meta charset="UTF-8">`	`<meta charset="UTF-8" />`
Link	`<link rel="stylesheet" href="style.css">`	`<link rel="stylesheet" href="style.css" />`

The trailing space and slash /> is what closes the empty element in XHTML.

Difference 7: Elements Must be in Lowercase

In HTML, tag names are case-insensitive · , , and  all work. In XHTML, all tag names must be lowercase.

XHTML Correct:

html

<body>
  <p>This is a paragraph</p>
</body>

XHTML Wrong:

html

<BODY>
  <P>This is a paragraph</P>
</BODY>

Difference 8: Attribute Names Must be in Lowercase

Just like element names, attribute names in XHTML must also be lowercase.

XHTML Correct:

html

<a href="https://www.example.com">Visit us</a>

XHTML Wrong:

html

<a HREF="https://www.example.com">Visit us</a>

Difference 9: Attribute Values Must be Quoted

In HTML, attribute values can sometimes be written without quotes. In XHTML, all attribute values must always be in quotation marks.

XHTML Correct:

html

<a href="https://www.example.com">Visit us</a>

XHTML Wrong:

html

<a href=https://www.example.com>Visit us</a>

Difference 10: Attribute Minimization is Forbidden

In HTML, some attributes can be written as just the attribute name alone · this is called attribute minimization. For example, the checked attribute on a checkbox, or disabled on an input.

In XHTML, every attribute must have a full name="value" pair · attribute minimization is not allowed.

XHTML Correct:

html

<input type="checkbox" name="vehicle" value="car" checked="checked" />
<input type="text" name="lastname" disabled="disabled" />

XHTML Wrong (minimized attributes · forbidden):

html

<input type="checkbox" name="vehicle" value="car" checked />
<input type="text" name="lastname" disabled />

3.4 · A Complete Comparison: HTML5 vs. XHTML 1.1

Here is a side-by-side comparison of the same page written in HTML5 and XHTML 1.1:

HTML5 version (flexible and modern):

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>My Page</title>
</head>
<body>
  <h1>Hello World</h1>
  <p>This is a paragraph.
  <p>This is another paragraph.
  <br>
  <img src="photo.jpg" alt="A photo">
  <input type="text" name="name" disabled>
</body>
</html>

XHTML 1.1 version (strict XML rules):

html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <meta charset="UTF-8" />
  <title>My Page</title>
</head>
<body>
  <h1>Hello World</h1>
  <p>This is a paragraph.</p>
  <p>This is another paragraph.</p>
  <br />
  <img src="photo.jpg" alt="A photo" />
  <input type="text" name="name" disabled="disabled" />
</body>
</html>

Key differences visible in the comparison:

DOCTYPE is much longer in XHTML
<html> tag has xmlns in XHTML
<meta> is self-closed with /> in XHTML
 tags have closing  in XHTML
  becomes   in XHTML
<img> is self-closed with /> in XHTML
disabled becomes disabled="disabled" in XHTML

3.5 · Should You Use HTML5 or XHTML Today?

For almost all modern projects: Use HTML5.

HTML5 is the current standard. It is powerful, flexible, well-supported by all browsers, and simpler to write. XHTML is no longer the recommended standard for new web projects.

However, XHTML's rules have lasting value:

Even though we use HTML5 today, following XHTML-style best practices makes your HTML much cleaner, more consistent, and professional:

Close all your tags
Write all tag names in lowercase
Always quote attribute values
Properly nest your elements

Many professional developers and coding style guides follow these XHTML-style conventions even when writing HTML5, because it leads to fewer bugs and more readable code.

Real-World Connection: Many server-side templating systems, XML parsers, and email HTML renderers (like those used for marketing emails) require XHTML-style well-formed HTML. Knowing XHTML rules means your HTML works correctly in ALL environments, not just forgiving web browsers.

✏️ Your Task

- XHTML is like a strict examiner · if you make any mistake at all, the document is considered invalid and may not work. ·

Phase 6 of 7

Part 4: Guided Practice Exercises

🎯 Your Challenge

Exercise 1 · Character Set Detective

Objective: Identify charset issues and fix them.

Scenario: Your friend built a webpage for a French restaurant. The page should display French accented characters like é, ê, à, ü, ç, but instead it shows strange symbols. You need to diagnose and fix the problem.

Broken page code:

✏️ Task

- What if you change the language to Yoruba and add:

Ẹ káàárọ̀! Ẹ káabọ̀!

· will UTF-8 still handle it? (Yes · UTF-8 covers Yoruba characters too!) ·

html

<!DOCTYPE html>
<html>
<head>
  <title>Restaurant Menu</title>
</head>
<body>
  <h1>Café Élysée</h1>
  <p>Spécialités du jour: Crème brûlée, Île flottante, Châteaubriand</p>
</body>
</html>

The Fix:

html

<!DOCTYPE html>
<html lang="fr">
<head>
  <meta charset="UTF-8">   <!-- ← Add this as the FIRST line inside <head> -->
  <title>Restaurant Menu</title>
</head>
<body>
  <h1>Café Élysée</h1>
  <p>Spécialités du jour: Crème brûlée, Île flottante, Châteaubriand</p>
</body>
</html>

Expected Output in browser:

code

Café Élysée
Spécialités du jour: Crème brûlée, Île flottante, Châteaubriand

All accented French characters display correctly now.

Self-Check Questions:

What was missing from the broken page?
Where exactly must <meta charset="UTF-8"> be placed?
Why did the accented characters fail to display without the charset declaration?

What-If Challenge:

What if you change the language to Yoruba and add: Ẹ káàárọ̀! Ẹ káabọ̀! · will UTF-8 still handle it? (Yes · UTF-8 covers Yoruba characters too!)

Exercise 2 · Decode a URL

Objective: Read and decode a URL-encoded string.

Scenario: You receive these URLs in a log file. Decode what the user was searching for.

URL 1:

code

https://example.com/search?q=World+Cup+2026

Decoded: World Cup 2026 (the + signs represent spaces)

URL 2:

code

https://example.com/search?q=Lagos%20music%20festival

Decoded: Lagos music festival (%20 = space)

URL 3:

code

https://shop.example.com/products?category=food%20%26%20drink&price=500

Decoded:

category = food & drink (%20 = space, %26 = &)
price = 500

URL 4:

code

https://example.com/weather?city=S%C3%A3o+Paulo

Decoded: city = São Paulo (%C3%A3 is the UTF-8 encoding of ã)

Exercise Task: Build a URL manually. Encode this search query for a URL parameter: naira & dollar rates 2026

Answer:

code

naira%20%26%20dollar%20rates%202026

or:

code

naira+%26+dollar+rates+2026

So the full URL would be:

code

https://example.com/search?q=naira+%26+dollar+rates+2026

Exercise 3 · HTML to XHTML Conversion

Objective: Convert an HTML5 page to valid XHTML.

Starting HTML5 code (has several XHTML violations):

html

<!DOCTYPE html>
<html>
<head>
<title>Student Records</title>
</head>
<body>
<H1>Student Records</H1>
<P>Welcome to the student portal.
<P>Please log in below.
<BR>
<IMG SRC="school-logo.png" ALT="School Logo">
<input type="text" name="username" PLACEHOLDER="Enter username">
<input type="checkbox" name="remember" checked>
<label for="remember">Remember me</label>
</body>
</html>

XHTML violations in the code above:

Missing xmlns attribute on <html>
Missing XHTML DOCTYPE
<H1> is uppercase · should be <h1>
 tags are uppercase AND not closed
  is uppercase and not self-closed
<IMG> is uppercase, not self-closed, SRC and ALT are uppercase
<input> has PLACEHOLDER in uppercase
checked is minimised (not checked="checked")

Corrected XHTML version:

html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <meta charset="UTF-8" />
  <title>Student Records</title>
</head>
<body>
  <h1>Student Records</h1>
  <p>Welcome to the student portal.</p>
  <p>Please log in below.</p>
  <br />
  <img src="school-logo.png" alt="School Logo" />
  <input type="text" name="username" placeholder="Enter username" />
  <input type="checkbox" name="remember" checked="checked" />
  <label for="remember">Remember me</label>
</body>
</html>

Self-Check Questions:

How many changes did you count between the two versions?
What is the key change for empty elements like   and <img>?
Why is checked="checked" used instead of just checked?

Phase 7 of 7

Part 6: Common Beginner Mistakes

Mistake 1 · Forgetting `<meta charset="UTF-8">` Entirely

Broken code:

html

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
</head>
<body>
  <p>Café, naïve, résumé</p>
</body>
</html>

Problem: Without a charset declaration, browsers may default to a legacy encoding and display CafÃ©, naÃ¯ve, rÃ©sumÃ© · complete nonsense.

Fixed code:

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">   <!-- ← Always include this! -->
  <title>My Page</title>
</head>
<body>
  <p>Café, naïve, résumé</p>
</body>
</html>

Mistake 2 · Placing `<meta charset>` Too Late in the `<head>`

Broken code:

html

<head>
  <title>My Page</title>
  <link rel="stylesheet" href="style.css">
  <script src="app.js"></script>
  <meta charset="UTF-8">   <!-- ← Too late! Browser may have already started decoding -->
</head>

Fixed code:

html

<head>
  <meta charset="UTF-8">   <!-- ← Must be first inside <head> -->
  <title>My Page</title>
  <link rel="stylesheet" href="style.css">
  <script src="app.js"></script>
</head>

Mistake 3 · Putting Spaces Directly in URLs

Wrong:

html

<a href="my page about dogs.html">Dog Page</a>

A space in a URL will break the link. The browser either truncates it at the space or produces an error.

Fixed:

html

<a href="my-page-about-dogs.html">Dog Page</a>

Use hyphens instead of spaces in file names and URLs. If you must pass a space in a query string, the browser will encode it automatically for form submissions, but in hand-coded URLs, you should use %20:

html

<a href="/search?q=dog%20training">Search for dog training</a>

Mistake 4 · Writing Uppercase Tags in HTML (Bad Habit from Old Code)

Old-style code (works but not best practice):

html

<BODY>
  <H1>My Heading</H1>
  <P>My paragraph.</P>
  <BR>
</BODY>

Modern HTML5 best practice (lowercase, XHTML-style):

html

<body>
  <h1>My Heading</h1>
  <p>My paragraph.</p>
  <br />
</body>

Lowercase tag names are standard, cleaner, and compatible with XHTML tools.

Mistake 5 · Forgetting to Close Empty Tags (Important for XHTML and Email HTML)

HTML5 (this is technically valid but not best practice):

html

<br>
<hr>
<img src="logo.png" alt="Logo">
<input type="text" name="email">
<meta charset="UTF-8">

XHTML-style (best practice · always self-close empty tags):

html

<br />
<hr />
<img src="logo.png" alt="Logo" />
<input type="text" name="email" />
<meta charset="UTF-8" />

This habit is especially important when building HTML emails (which are rendered by email clients that expect XHTML-style markup) or working with XML-based systems.

Mistake 6 · Not Quoting Attribute Values

Wrong:

html

<a href=https://example.com>Visit</a>
<img src=photo.jpg alt=My Photo>

Fixed:

html

<a href="https://example.com">Visit</a>
<img src="photo.jpg" alt="My Photo" />

Always quote every attribute value. Unquoted values break in XHTML and can cause unpredictable behavior in HTML when the value contains spaces.

Mistake 7 · Misreading URL Encoded Characters

Common confusion: Seeing %20 in a URL and not knowing what it means.

code

https://example.com/search?q=web%20development%20course
                                 ↑                ↑
                               %20 = space      %20 = space

Decoded: The user searched for web development course.

Another common one:

code

https://example.com/login?redirect=%2Fdashboard
                                    ↑
                                  %2F = /

Decoded: Redirect to /dashboard after login.

✏️ Your Task

`html

My Heading

My paragraph.

` Modern HTML5 best practice (lowercase, XHTML-style): `html

My Heading

My paragraph.

` Lowercase tag names are standard, cleaner, and compatible with XHTML tools. ·

🏗️ Build It — Mini Project

Stage 1 · Build the HTML Structure

You will now build a complete, professional-quality multilingual contact page. It will correctly declare UTF-8, display text in multiple languages, build a working URL query string, and follow XHTML-style best practices throughout.

Stage 1 · Build the HTML Structure

Create a file called contact.html:

starter.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Global Contact Page</title>
</head>
<body>

  <header>
    <h1>Global Contact Page</h1>
    <p>Reach us in your language — we speak many!</p>
  </header>

  <!-- Multilingual Greetings Section -->
  <section>
    <h2>Greetings from Around the World</h2>
    <ul>
      <li>🇬🇧 English: <strong>Hello, World!</strong></li>
      <li>🇫🇷 French: <strong>Bonjour le monde!</strong></li>
      <li>🇳🇬 Yoruba: <strong>Ẹ káàbọ̀! (Welcome!)</strong></li>
      <li>🇸🇦 Arabic: <strong>مرحبا بالعالم</strong></li>
      <li>🇨🇳 Chinese: <strong>你好，世界！</strong></li>
      <li>🇧🇷 Portuguese: <strong>Olá Mundo!</strong></li>
      <li>🇩🇪 German: <strong>Hallo Welt!</strong></li>
      <li>🇯🇵 Japanese: <strong>こんにちは世界！</strong></li>
    </ul>
  </section>

  <!-- Contact Form Section -->
  <section>
    <h2>Contact Us</h2>
    <form action="/contact-submit" method="GET">

      <label for="name">Full Name:</label><br />
      <input type="text" id="name" name="name" placeholder="Enter your full name" /><br /><br />

      <label for="email">Email Address:</label><br />
      <input type="email" id="email" name="email" placeholder="you@example.com" /><br /><br />

      <label for="country">Country:</label><br />
      <input type="text" id="country" name="country" placeholder="e.g. Nigeria" /><br /><br />

      <label for="message">Message:</label><br />
      <textarea id="message" name="message" rows="5" cols="40"
        placeholder="Type your message here..."></textarea><br /><br />

      <label>
        <input type="checkbox" name="subscribe" value="yes" />
        Subscribe to our newsletter
      </label><br /><br />

      <button type="submit">Send Message</button>

    </form>
  </section>

  <!-- URL Encoding Demonstration -->
  <section>
    <h2>How Your Data Travels in the URL</h2>
    <p>When you submit this form, your browser encodes your input into a URL like this:</p>
    <code>
      /contact-submit?name=Jane+Doe&amp;email=jane%40example.com&amp;country=Nigeria&amp;message=Hello%21&amp;subscribe=yes
    </code>
    <p>Notice: <code>@</code> becomes <code>%40</code>, spaces become <code>+</code>,
       <code>!</code> becomes <code>%21</code>,
       and <code>&amp;</code> separates each field.</p>
  </section>

  <footer>
    <p>&copy; 2026 Global Contact Page. Charset: UTF-8. Built with clean HTML.</p>
  </footer>

</body>
</html>

How Your Data Travels in the URL

When you submit this form, your browser encodes your input into a URL like this:


      /contact-submit?name=Jane+Doe&email=jane%40example.com&country=Nigeria&message=Hello%21&subscribe=yes

Notice: @ becomes %40, spaces become +, ! becomes %21, and & separates each field.

`)" style="background:#10b981;box-shadow:0 4px 14px rgba(16,185,129,.3)">Download starter.html ↓

Lesson 30 complete! 🎉

You covered:

✅ Lesson Introduction
✅ Prerequisite Concepts
✅ Part 1: HTML Character Sets (Charsets)
✅ Part 2: URL Encoding
✅ Part 3: HTML vs. XHTML
✅ Part 4: Guided Practice Exercises
✅ Part 6: Common Beginner Mistakes

← Lesson 29 Lesson 31 →

HTML Charsets, URL Encoding, and XHTML

👋 Welcome to Lesson 30

What is a Bit and a Byte?

What is a Character?

What is Encoding?

1.1 · Why Browsers Need to Know the Character Set

1.2 · The History of Character Sets: From ASCII to UTF-8

Stage 1: ASCII · The Original Internet Character Set

Stage 2: ANSI (Windows-1252)

Stage 3: ISO-8859-1 · The Default for HTML 4

Stage 4: UTF-8 · The Universal Standard

1.3 · The Unicode System and UTF-8

1.4 · Character Set Quick Reference Table

1.5 · A Sample of UTF-8 Character Groups

1.6 · Where to Put the charset Declaration

2.1 · What is a URL?

2.2 · The Anatomy of a URL

2.3 · Common URL Schemes

2.4 · Why URL Encoding Exists

2.5 · How URL Encoding Works

2.6 · Real-Life URL Encoding Examples

2.7 · ASCII Encoding Examples by Character Set

2.8 · How URL Encoding Appears in Practice

3.1 · What is XHTML?

3.2 · Why Was XHTML Created?

3.3 · The Nine Key Differences: HTML vs. XHTML

Difference 1: <!DOCTYPE> is Mandatory in XHTML

Difference 2: The xmlns Attribute in <html> is Mandatory

Difference 3: <html>, <head>, <title>, and <body> are All Mandatory

Difference 4: Elements Must Always be Properly Nested

Difference 5: Elements Must Always be Closed

Difference 6: Empty Elements Must Always be Closed

Difference 7: Elements Must be in Lowercase

Difference 8: Attribute Names Must be in Lowercase

Difference 9: Attribute Values Must be Quoted

Difference 10: Attribute Minimization is Forbidden

3.4 · A Complete Comparison: HTML5 vs. XHTML 1.1

3.5 · Should You Use HTML5 or XHTML Today?

Exercise 1 · Character Set Detective

Exercise 2 · Decode a URL

Exercise 3 · HTML to XHTML Conversion

Mistake 1 · Forgetting <meta charset="UTF-8"> Entirely

Mistake 2 · Placing <meta charset> Too Late in the <head>

Mistake 3 · Putting Spaces Directly in URLs

Mistake 4 · Writing Uppercase Tags in HTML (Bad Habit from Old Code)

Mistake 5 · Forgetting to Close Empty Tags (Important for XHTML and Email HTML)

Mistake 6 · Not Quoting Attribute Values

Mistake 7 · Misreading URL Encoded Characters

My Heading

My Heading

Stage 1 · Build the HTML Structure

Greetings from Around the World

Contact Us

How Your Data Travels in the URL

Lesson 30 complete! 🎉

1.6 · Where to Put the `charset` Declaration

Difference 1: `<!DOCTYPE>` is Mandatory in XHTML

Difference 2: The `xmlns` Attribute in `<html>` is Mandatory

Difference 3: `<html>`, `<head>`, `<title>`, and `<body>` are All Mandatory

Mistake 1 · Forgetting `<meta charset="UTF-8">` Entirely

Mistake 2 · Placing `<meta charset>` Too Late in the `<head>`