This is a silly question really, but I couldn’t find it in the documents, but what is that slide with the number and name of the subtool(next to R, restores number of visible items to a default configuration.
Any idea?

This is a silly question really, but I couldn’t find it in the documents, but what is that slide with the number and name of the subtool(next to R, restores number of visible items to a default configuration.
Any idea?

The Item Info slider is just Zbrush’s way of letting you select through a massive list (of Tools in this case). You’ll find similar sliders under Alphas, Brushes, Materials, Strokes, and Textures, and they share the same purpose.
They can come in handy when it comes to zscripting, in case you want to cycle through to the next item in the list (or all of them), store the current item, select the last one, etc.
Yeah,I knew it wasn’t part of lightbox, but rather just sat underneath it, just for location reasons I listed it as such.
When I slid it, it gave the message with my scene, "The active tool is currently in EDIT/TRANSFORM mode.
Would you like to exit EDIT/TRANSFORM mod and switch tools?
I had never seen this in use before. Not sure why I’d ever need this as it closes my current “tools” or rather mesh I’m working on.
You get that message because you switched to a 2.5D tool that doesn’t have edit mode. It’s really no different than if you were to have clicked on one of the Tool Palette thumbnails (such as the ‘SimpleBrush’ icon) instead of the slider. If you were to use either the slider or the thumbnails to select another 3d model then there would be no such message; the new tool would be instantly active, in edit mode, with the same view.
If you’re working on a single tool then you likely won’t need this option - or any option - to switch tools (the same way someone who only uses the move brush won’t want to select any of the other hundred brush types available to them). Its more useful for people who use multiple tools in their work.
Even when primarily working on a single tool it still has its uses. For example, a script that lets you re-position a subtool by snapping two vertices together would make use of this Item Info slider in order to store the current tool, preform a merge visible operation and automatically switch to this new tool so that the user can select the two vertices they want to use, and it will know to switch back to the original tool in order to apply the appropriate transformation values.