Relative URLs
Description
If the value of the href attribute doesn't start with
a recognized protocol, such as http://,
then the browser treats the hyperlink as a relative reference.
Example
The following code gives an example of a relative URL.
<!DOCTYPE HTML>
<html>
<body>
I like <a href="index.html">tutorial</a>.
</body>
</html>
The code set the href attribute to index.html.
When the user clicks the link, the browser uses the URL of the current document to determine how to load the linked page.