The above description of the W3.js file is contained in another file and is included here by using the W3.js Library. How to do HTML includes using this library can be seen by looking at the source code of the current page and is discussed at https://www.w3schools.com/howto/howto_html_include.asp
Looking at the current page in Dreamweaver in Design view will not show the content of the included file, but this content is visable in Live View.
Revised: November 7, 2017