1. I meant mouse middle click, I think this is pretty standard terminology.
3. You are right, the video could be a lot better. You are not really supposed to read the texts though, the main purpose is to showcase the features.
Well, for a lot of people, e.g., a big fraction of the HN audience, sure, okay.
But: Yup, way back when personal computers were starting to use a mouse, there was no "middle click". Then there was, as a step forward -- I remember that. Now here is a surprise: While I spend well over 40 hours a week at a keyboard looking at a screen driven by Windows with data mostly from the Internet, I have not heard of or used the mouse middle click in years. The main reason is that on Windows, at least with the options I have, all the middle click is good for is a fast version of vertical scrolling on the contents of a window on the screen, and I don't find that fast scrolling to be useful. So, I have just forgotten about middle clicking. I'm up on a LOT of old stuff in computing, a lot of it from way back before middle clicking, but not middle clicking -- I just didn't find it useful. Here I'm using my experience as evidence for a
Lesson: In making assumptions about what is "pretty standard" for your users, it is tough to be accurate and for a solution work to err on the side of assuming less, a lot less.
There is one more point: It is totally obscure to me how fast scrolling could play much role in tracing references in PDF files of math. Maybe the Windows Win32 API permits programs to treat the middle click and scroll wheel any way it wants. If so, then that is something else tough to assume users know and be accurate. E.g., from my experience, I've written a lot of software and a lot for Windows .NET but so far I've never written any code that directly called the Win32 API. So, I have no good knowledge on what might be in Win32 for middle clicking.
Lesson: "pretty standard terminology", I wouldn't assume that.
More generally I claim that computing is being badly hurt by way too little in definitions for way too much technical jargon.
There is a simple solution: When in doubt, and even if not, work to define or at least give a reference for technical jargon. E.g., here at HN (Hacker News) apparently (although I've seen no statement) OP abbreviates "original post".