SILS iSchool

week of 16 February 2021

Value Added | daily

Class Schedule

Basics | sessions 01-03
  1. 19 Jan intro and clients | lecture | labs
  2. 26 Jan servers and command line | lecture | labs
  3. 02 Feb networks and protocols | lecture | labs
Web Development | sessions 04-08

  1. 09 Feb structural layer | lecture | labs
  2. 16 Feb presentational layer | lecture | labs
  3. 23 Feb using a structure | lecture | labs
  4. 02 Mar behavioral layer | lecture | labs
Dealing with Markup | sessions 09-10
  1. 16 Mar control objects and display | lecture | labs
  2. 23 Mar tools that read markup | lecture | labs
Working with data | sessions 11-14
  1. 30 Mar formulas, functions, vectors | lecture | labs
  2. 06 Apr data display | lecture | labs
  3. 13 Apr manipulate data sets | lecture | labs
  4. 20 Apr relational data bases | lecture | labs
Presentations | sessions 15-16
  1. 27 Apr designing a presentation | lecture | labs
  2. 04 May delivering a presentation | lecture | labs

"Presentational" means the rules that define the visual aspects of how a web document is displayed on a computer monitor.

CSS - the presentational layer

Cascading Style Sheets (CSS) is a W3C standard for defining the presentation of web documents

We will define "presentation" as meaning the visual aspects of how a web document is displayed on a computer monitor. If you create a web page, it will display as you instructed it to display, even if you inadvertently instructed it to display as someone else instructed it.

To be a bit more clear,

each HTML tag has to display in some fashion
and a browser looks for instructions telling it how to display the tag.
If it finds none, it will display the element according to the browser's own display rules

For example, this page shows how several basic tags display when the page provides no specific instructions telling it what to do. In this case, the browser defaults to its own set of display rules.

The second example is the same HTML, but has a link in line 08 of the code to the CSS stylesheet for the INLS161-001 website.

The third example is the same HTML, but has a link in line 12 of the code to a second CSS stylesheet.

Toggle back and forth to see the difference.

These display rules can be applied to one or more pages and then any change made to the rules will apply to all pages linked to the rules.

W3Schools has a similar example.

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Let's look at this page in terms of its CSS elements and rules

screenshot of the current page viewed in Chrome developer view

If you right click and open the image in a new tab, you can see how the sidebar is a <div> element, with specific CSS instructions telling it how to display.

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Benefits of CSS

Greater typography and page layout controls

Greater control over how your type displays; you can be explicit in your definitions

Less work

One edit, multiple simultaneous corrections; really useful in a large site

Potentially smaller documents

You need only create a link to a single list of rules, rather than recreate the rules in each page you create.

Let's go back and look at our MSWord-created page for a comparison. It has all the display rules for all the possible tags embedded in the page file.

Potentially more accessible documents

Though it is easier to control the placing of objects on a web page using visual tools such as tables, such tables are not always useful for all users.

CSS guidelines allow you to build pages that are accessible by a far wider span of potential users.

Presentational HTML is on its way out

Mixing the rules about what an object means and how it should look on a single page is a thing of the past.

Even though current browsers still support such activities, eventually they will drop this ability and all pages will need to conform to the CSS standard

You will follow CSS rules for your task 02, so it would be a good idea to get used to them now

CSS is well-supported

The CSS3 specification is the latest complete standard for Cascading Style Sheets. CSS3 is completely backwards-compatible with earlier versions of CSS.

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week of 16 February | preps | presentational layer | in practice | planning