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Comment tags (contd.)

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>

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Comment tags (contd.)

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  1. 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.

  2. <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>

  3. Using <IMG> tags

  4. <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

  5. <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” >

  6. A simple web document containing a picture

  7. Of course, we can have text with the pictures

  8. A document

  9. 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

  10. 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

  11. Background colour (contd.) • For example, consider how the last document we specified would appear in both Netscape Navigator and Microsoft Explorer

  12. 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

  13. 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

  14. 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

  15. 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

  16. Another kind of list: Definition lists

  17. Definition lists: • Frequently, we want to have lists of items like this: CPU Central Processor Unit VDU Visual Display Unit IRQ Interrupt ReQuest

  18. 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

  19. 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>

  20. 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>

  21. 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>

  22. 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>

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