• HyperText Markup Language:
    • Hypertext is a document interconnected with other documents via links.
  • The most used format of web pages (documents provided by WWW service).
  • The last version of the standard – HTML5 from 2014 – W3C Specification.
  • HTML is a language for describing the structure of a text document.
  • HTML is not a programming language.
  • HTML is interpreted by Web Browsers.

Web Browsers

Graph -- Browser Share

HTML Structure

  • Hierarchical structure of elements:
    • parentchild relationship (siblings too).
  • Elements are written down using tags:
    • <h1 id='intro'>Introduction</h1>
  • Element:
    • Name (enclosed in angle brackets) – h1,
    • Start tag – <h1>,
    • End tag – </h1>,
    • Body – Introduction,
    • W3C Specification.

HTML Structure

  • <h1 id='intro'>Introduction</h1>
  • Elements can have attributes:
    • Additional properties of the element,
    • Entered in the start tag in arbitrary order (delimited by space),
    • Name – id,
    • Value – intro,
    • W3C Specification.

HTML Structure

  • Entities – placeholders for special characters:
    • Begin with the ampersand &, end with the semicolon ;,
    • Encoded as:
      • a symbolic character name – &gt; (greater) – defined in W3C Specification,
      • or a numeric Unicode character code reference – &#62; or &#x3E;,
  • Comments – a part of the HTML code which is not interpreted:
    • <!-- a comment may not contain two dashes -->,
    • They are still visible in the page source!
  • Unless you do something special, all browsers generally do behave the same way.

HTML Example

        <TITLE>Page Title</TITLE>
    <BODY ID=main>
        <p>Hello World!
            <LI class=main><P>First!
            <LI><P>second list item

Better HTML Example

<!DOCTYPE html>
        <title>Page Title</title>
        <meta charset="utf-8">
    <body id='main'>
        <p>Hello World!</p>
            <li class='main'><p>First!</p></li>
            <li><p>second list item</p></li>

HTML Elements

  • Block-level elements – P, H1, DIV, …
  • Inline elements – A, IMG, SPAN, …
  • Inline elements may be inserted in inline elements or block elements.
  • Block elements may be inserted only inside block elements.
    • With the exception of A.

HTML Attributes

  • Common attributes:
    • id, class – used for styling and scripting on the client side,
    • style – definition of an inline style,
    • title – hint which is shown on mouse-over,
    • others –,
    • data attributes – arbitrary attributes without semantics.
  • Containment principle – related to the page layout.

HTML Elements – Oddities

  • Empty elements (have no body):
    • <img src=''> – valid,
    • <img src='' /> – also valid,
    • <img src=''></img> – also valid but not recommended.

HTML Elements – Oddities

  • Boolean attributes:
    • <input type='text' required> – valid True,
    • <input type='text' required='required'> – valid True,
    • <input type='text' required='1'> – invalid True,
    • <input type='text' required='0'> – completely wrong,
    • <input type='text' required='false'> – completely wrong,
    • <input type='text'> – valid False.

HTML Header

  • a head element may contain:
    • title – set page title (required),
    • meta – set page metadata, at least encoding:
      • <meta charset='utf-8' /> (almost required)
    • style – CSS styles in the page,
    • link – a definition of related files (external style, fonts, etc.),
    • script – a JavaScript code or a link to a JavaScript code.


  • XML (Extensible Markup Language) – a generic language for data description.
  • Looks similar to HTML – the same ancestor (SGML):
    • contains elements, attributes, entities,
    • does not define interpretation or rendering of data.
  • Simplified rules:
    • required header: <?xml version="1.0"?>,
    • a tag name is lower-case, the end tag is required
    • an attribute value must be in quotes, a value is required,
    • an empty tag may be shortened to <element />,
  • An XML Application is an interpretation of the XML document (not a program).

XML Example

<?xml version='1.0' encoding='utf-8' ?>
    <name last_modified='1.2.2007'>category1</name>
    <caption>First category</caption>
    <description />
            <caption>First Sub-category</caption>
            <caption>Next Sub-category</caption>


Various HTML related Standards


  • HTML4 has:
    • many optional language elements (the language was supposed to be smart),
    • complicated implementation of an interpreter in a web browser,
    • semantic elements and visual elements,
    • <!DOCTYPE that specifies the DTD.
  • XML has:
    • faster and more effective processing than HTML,
    • simple parser implementation.
    • no error recovery


  • XHTML:
    • is an XML application of the HTML language,
    • has supposedly simplified interpreter implementation,
    • has no error recovery if transmitted as application/xhtml+xml,
  • HTML5:
    • is a brand new language without a lot of historic burden,
    • is developed from 2007, standardized in 2014,
    • is not based on SGML,
    • has complicated implementation of an interpreter.
    • contains both HTML and XHTML markups (and HTML DOM) representations


  • <!DOCTYPE html>
  • Extended semantic elements (article, nav, menu, …).
  • Improved user interaction:
    • inserting objects into the page (video, vector graphics, math, …),
    • improved form elements (date, number, …),
    • validation of forms (data types, regexp, …),
    • spread forms (form elements without containment),
    • data attributes.
  • Removed all visual elements.
  • Done some accessibility improvements (see WCAG).
  • Extensible with other markups (MathML, SVG).


  • HTML describes only the structure of a text document.
    • There is no way to change the visual rendering.
  • To change the rendering of a document, styles must be used.
  • CSS (Cascading Style Sheets) is a language for the definition of styles.
    • CSS is not a programming language.
  • When no styles are applied, the web browser uses default styles (also called user-agent styles).

CSS Styles

CSS Styles

  • Dozens of modules:
    • font properties, color, box properties, box model,
    • border, color, margin, background, effects, …
  • Web page is not paper.
    • Web page must adapt to (almost) infinite number of window sizes.
    • Leads to Responsive design.
    • Requires a good page layout in HTML as well.

CSS Syntax

  • A CSS document is composed of CSS rules:
    • selector {property: value;}
  • Example: body {color: black;}
    • There is no semicolon after the parentheses.
  • Selector:
    • element name – h1 {color: white}
    • element class – .table_list {width: 100%}
    • element id – #input_name {width: 40px}
  • Selectors can be combined.
  • Any number of properties can be set in a single rule.

CSS Syntax

  • Selector combinations examples:
    • li, a – for an element that is either <li> or <a>,
    • li a – for an element <a> that is contained in <li>,
    • li>a – for an element <a> that is a direct child of <li>,
    • – for an element <li> that has the class menu.
  • Pseudo-classes:
    • things which cannot be determined by HTML structure,
    • hover, active, focus, link, visited, nth-child, …
    • li a:visited – a visited link inside an li,
    • a#first:link – a not visited link with id first inside an li with the class menu.

Connecting styles with HTML

  • External file:
    • <link rel='stylesheet' href='style.css'>
    • The best solution – all styles in one place.
    • a link to the HTML element with selectors (element name, class, id).

Connecting styles with HTML cont.

  • Inside HTML page:
    • <style type='text/css'>body {color: green;} … </style>
    • Used for special pages.
    • Used to optimize the number of HTTP requests.
  • Inline:
    • <body style='color: green'>…
    • (Obviously?) without a selector.
    • Highest priority, use only for exceptions.

Styles example

<style type="text/css">
    body {color: grey; background: #eeeeee;}
    h3 {background: #cccccc; color: red;}
    .blue {color: blue;}
    #unique {color: white;}
    h3.colored {color: magenta;}
    .black {color: black}
    <h3 class='blue'>second</h3>
    <h3 id='unique'>third</h3>
    <h3 class='colored'>fourth</h3>
    <h3 class='colored blue'>fifth</h3>
    <h3 class='blue black'>sixth</h3>

Cascading Styles

  • Style properties are inherited from parent elements to child elements:
    • the top element is body (in rare cases html);
    • not all properties are inherited (use common sense).
  • All CSS rules are applied in order by priority:
    • closer and more specific rules have higher priority;
    • higher priority rules override lower priority rules;
    • only properties are overridden, not entire rules.
  • Inline style > page style > external style.
  • Id > class.

CSS Box Model

  • Padding – inside of the HTML element – between the content and the box.
  • Border – outside of the HTML element – around the box.
  • Margin – outside of the HTML element – around the box.

Margin & Padding

CSS Box Size

  • Size – width/height - content + spacing + border.
  • The size is depending on the box model:
    • basic types: inline, block (corresponding with HTML elements);
    • inline is limited by the line size;
    • the block is sized independently.

CSS Colors

  • On screen, colours are mixed additively.
  • A color can be set by:
    • name – black, white, … (over a hundred);
    • by three RGB components (component intensity 0-255):
      • color: rgb(255, 0, 0) (decimal),
      • color: #FF0000 (hexadecimal),
      • color: #F00 (shorthand hexadecimal),
      • color: rgba(255, 0, 0, 0.5) (alpha channel);
    • by three HSL components:
      • color: hsl(0, 100%, 50%),
      • color: hsla(0, 100%, 50%, 0.5) (alpha channel).

CSS Layouts

  • Creating a full page layout is a non-trivial task.
  • Layouts for web pages and for web applications are completely different.
  • Use existing layouts, e.g.:
  • Complicated layouts use alternatives to CSS (LESS, SASS).
    • Must be compiled to CSS for web browsers.



  • Why mustn’t the HTML start tag and end tag cross?
  • What happens if a HTML document lacks a <!DOCTYPE?
  • Can you have a delete icon on a page without using an image?
  • What does XML and HTML have in common?
  • Why CSS3 has not been standardized yet?
  • Who says that <title> must not occur twice in a HTML document?
  • Is it better to draw a border using CSS or use an PNG image?
  • What does HTML4 and HTML5 have in common?