Comment tags (contd.) A comment tag is of the form A comment can appear anywhere in a html...
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Transcript of Comment tags (contd.) A comment tag is of the form A comment can appear anywhere in a html...
Comment tags (contd.)
• A comment tag is of the form<!-- Some-comment-text-appears-here -->
• A comment can appear anywhere in a html specification
• They are frequently used to tell people who wrote the specification, when, why, etc.
<html>
<head>
<title> Politics in Ireland </title>
<base href=“http://www.iol.ie/pres/”>
<!-- Written by: James Bowen Date: 19/10/2000 Why: CS4400 class -->
</head>
<body>
<h1> Presidents </h1>
<p>
The presidents of Ireland were </p>
<ol>
<li> <A href="hyde.htm"> Douglas Hyde </A>
<li><A href="dev.htm"> Eamon de Valera </A>
</ol>
</body>
</html>
<img> tags
• <img> tags are used to incorporate pictures into web documents
• A picture cannot be inserted directly into the html spec of a web document, since a html spec is a textual spec
• <img> tags are used to point to pictures that we want to appear in a web document
<img> tags (contd.)
• The <img> tag is a structured tag -- it has attributes
• The src attribute is used to point to the picture to be included
<img src = “some-URL” >
• Use lower-case tags and attributes
– The picture on this slide is very old
– It shows upper-case tags and attributes, which were allowed back then
– Upper-case tags and attributes are not allowed any more
– Do not use upper-case tags or attributes
• Use lower-case tags and attributes
– The picture on this slide is very old
– It shows upper-case tags and attributes, which were allowed back then
– Upper-case tags and attributes are not allowed any more
– Do not use upper-case tags or attributes
• Use lower-case tags and attributes
– The picture on this slide is very old
– It shows upper-case tags and attributes, which were allowed back then
– Upper-case tags and attributes are not allowed any more
– Do not use upper-case tags or attributes
The ALIGN attribute• In early versions of html, img tags used to
have an ALIGN attribute for specifying how to align pictures relative to neighbouring text
• This was, therefore, a rendering attribute
• DO NOT USE this attribute– NEVER use rendering attributes
• We will see how to achieve rendering effects more cleanly when we meet Style Sheets
Colour of the background
• It would be preferable if you could ignore such rendering features as the colour of the background
• Unfortunately, when you start using pictures, you cannot, since pictures have colour and you have to consider how clearly an image will show up against the background
Background colour (contd.)
• For example, consider how the last document we specified would appear in both Netscape Navigator and Microsoft Explorer
Background colour (contd.)
• In Netscape, the images show up clearly against the default background colour, which is white
• In Explorer, the largely-grey images do not contrast so well with the grey-ish background
Background colour (contd.)
• We can specify the background colour we want
• Early versions of html provided a BGCOLOR attribute in the <body> tag
• However this is a rendering attribute and SHOULD NOT BE USED
• We will see how to do it more cleanly when we meet style sheets
Background PATTERNS
• We can also ask the browser to use a repeated version of some image as a background
• This should be done with care, because– it can lead to unreadable documents– it adds to the length of time it takes to
download a document over the Internet
Background PATTERNS
• Early versions of html provided an attribute in the <body> tag for this purpose
• Again, as with all rendering attributes, DO NOT USE IT
• We will see how to do achieve the same effect more cleanly when we meet style sheets
Definition lists:
• Frequently, we want to have lists of items like this:
CPUCentral Processor Unit
VDUVisual Display Unit
IRQInterrupt ReQuest
• In other words, we want to have a list in which each member has two parts:– a TERM, whose meaning is to be defined– a DEFINITION of the term
• html provides a tag for this kind of concept: the Definition List tag or <dl> tag
• A list of definitions is delimited by a <dl> tag and a </dl> tag
<dl>
….
….
</dl>
• Each item between the <dl> and </dl> tags has two parts, a term and its definition
• A term is delimited by <dt> and </dt> tags, while a definition is delimited by <dd> and </dd> tags:<dl>
<DT > CPU </dt> <dd> Central Processing Unit </dd>
<dt> VDU </dt> <dd> Visual Display Unit </dd>
<dt> IRQ </dt> <dd> Interrupt ReQuest </dd>
</dl>
• Example document:
<html>
<head>
<title> Definition List </title>
</head>
<body>
<h1> Some Computing Acronyms </h1>
<dl>
<DT > CPU </dt> <dd> Central Processing Unit </dd>
<dt> VDU </dt> <dd> Visual Display Unit </dd>
<dt> IRQ </dt> <dd> Interrupt ReQuest </dd>
</dl>
</body>
</html>
• Another example document: <html>
<head>
<title> Languages of the World </title>
</head>
<body>
<h1> Languages of the World </h1>
<dl>
<dt> Tok Pisin </dt>
<dd> A Melanesian Creole spoken in the South-western Pacific </dd>
<dt> Hakka </dt>
<dd> One of the languages spoken in Fujien province in China</dd>
<dt> Mon </dt>
<dd> A language spoken in Cambodia</dd>
<dt> Xhosa </dt>
<dd> One of the major languages of South Africa</dd>
</dl>
</body>
</html>