For complete information about this web page, see this instruction page.
The two scrollPlaceholder '-main' and two scrollPlaceholder '-mini' versions will add a 'temporary id' to all 'img' (image) tags on a web page that lack a native 'id' attribute. (The 'id' uniquely identifies each 'img' tag on a web page.)
All four '-main' and '-mini' versions perform other activities behind the scenes, as the instruction page will explain.
Note:You can toggle the “page-positioning” of the “Mini Scroller” between the default “fixed” setting and an “absolute” setting by clicking the “A/F” button above the “Mini Scroller.” The “fixed” setting keeps the “Mini Scroller” from moving while you are scrolling the web page up and down; while the “absolute” setting allows the web page to take the “Mini Scroller” along for the ride! This allows you to experiment with all of the different scenerios for toggling between the red “Mini Scroller” images, and their grey, bandwidth-saving 'placeholder' image replacements.