One of the ways that site builders test how their users interact with their pages is through click- and mouse-tracking.
Essentially, as you go through the page, every sweep of the mouse and click are recorded and sent back to the website to help
evaluate how well the design works.
And of course, other site builders use this information for other, less savoury purposes.
← onclick event
Double click this!
← ondblclick event
← onkeypress event
Loading Ms. PacMan... ← onload event
← onmouseover event
← onerror event
Saving your work
After playing with this page, pop open the context menu with your mouse and choose View page source.
Read over the code and try to link the HTML elements with the functions defined in the <script> block in the <head>.
Then create your own page that changes elements of the page based on user interactions.