Showing invisible characters and tags
Web pages are written in HTML. Much of this language is not displayed on the screen but is used to instruct the browser. Sometimes to understand what is happening it is useful to load the HTML document into a text editor. As a page becomes more and more complex this can be a very depressing activity so it is rarely attempted by anyone but the more expert developers.
For the rest of us it is usually enough to be shown the invisibile characters. These characters uncover the real structure of the page.
Most users will never need to use invisible characters at all.
To see invisibles select View > Tags from the window menu.
Here is an example of invisible tags