Finding the Priority Column

Hey everyone, I'm a complete beginner in R and had came across some confusion. I was using the installed.packages() function to see what packages automatically came with RStudio. I found that every value in the "Priority" column was NA. I researched online and a user on Stack Overflow said that we must do the following: installed.packages(priority = "high"). I tried this out and I was able to see what packages has a "base" or "recommended" priority.

My question: Why is the default in the "Priority" column NA? Is that just how RStudio is and there's no real explanation for it? Also, what exactly does "high" represent? What exactly does that "high" mean that causes it to help us achieve our result? Thank you.

This is not an RStudio thing, it is an R/CRAN thing. From https://cran.r-project.org/doc/manuals/R-exts.html:

Base and recommended packages (i.e., packages contained in the R source distribution or available from CRAN and recommended to be included in every binary distribution of R) have a ‘Priority’ field with value ‘base’ or ‘recommended’, respectively. These priorities must not be used by other packages.