24 August 2021

    caching of pages
         Your browser keeps stuff it downloads in memory.

    IP number:  Internet Protocol. This is your "phone number" during an
        internet session.  
    Mac number:  This a unique ID for your machine.
    DNS: Domain name server.  
        the internet only groks IP addresses
        Your machine maintains a local DNS cache which stores IPs for 
            recently visited sites.
        If a site is not in there, the browser will query your ISP's DNS cache.
        If this fails, there are DNS servers on the web the browser can check.

    DNS and DNS caches: machine, ISP, web

HTML

Our Environment We are going to do a lot of editing in here, so let's get things set up.

Open VSCode.
Select File → New File
Save the file as first.html in your folder for this class.
Open your browser and choose File → Open....
You will now be able to view your (empty) file

This is a shell HTML file. Save a copy as shell.html and you can copy it to do other projecrs. This will save you typing.


<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>My First Page</title>
    </head>
    <body>
        <h1>My First Page</h1>
        <p>This is  a paragraph of text.  </p>
        <p>This is  another paragraph of text.  </p>
    </body>
</html>

You will see that there are really three things in HTML, tags, text, and attributes.

Tags come in three types.

<foo> This is an opening tag. It defines the start of an HTML element.
</foo> This is an closing tag. It defines the end of an HTML element.
<foo/> This is a self-closing tag. The most common one you will see is for images or the certain tags that occur in the head of a document.

Grammar Rule Tags should close in the reverse order that they open. Documents meeting this specification run predictably and efficiently. Such documents are said to be well-formed.

Activity

Do the first.html activity on the specs page.