Figuring out subtitle files/folders with VLC: .SRT and .SUB and .IDX

[tzx613]

Hi, I'm trying to figure out how the whole subtitle file/folders/subfolders thing works with VLC on Windows. Normally I always worked with .SRT files for subtitles and I'd have two options to get the subtitle to work with the video:

1. Open the video on VLC and select Subtitle > Add subtitle file > select the .SRT file.
2. Rename the .SRT file to the same as the video file, then open the video file.

But right now, I've got this folder full of a bunch of videos, and then inside that folder with the videos, is another folder called "Subs" and inside this folder are a bunch of .SUB and .IDX files. These .SUB and .IDX file names do not match the video file names. Yet, somehow, when I play the videos with VLC the subtitles do work correctly. And if I move or modify these files or the "Subs" folder in any way, the subtitles no longer work.

I was wondering, what exactly is going on here? Do .IDX and .SUB files work differently than .SRT files? Can I also make a folder called "Subs" and shove all my .SRT files in there instead of having them all right underneath my video files? What about the naming of the .SUB and .IDX files? How are the video files "recognizing" these files if they are named differently?