Are vignettes build in a fresh R session when building a package?

Question

I have read Hadley guide to vignettes and I can't find any information about this. How are the vignettes build? My problem is that it seems that they are build with the suggested packages attached and loaded.

As far as I could test, if I knit it on the console in Rstudio it uses the same environment as the console.

I digged into devtools::build_vignettes but it seems to depend on tools::buildVignettes which I can't understand and seems like the default used when building a package with R CMD build .

This is related to my efforts to solve this question

Answer 1

When building the package the environment for all the vignettes is shared. So if vignette V1 loads package A, B and C, it will be already loaded for vignette V2 if V2 is build before V1.

That was what I learn from Martin Morgan at Bioconductor mailing list . I couldn't find any other document explaining it.