[Rd] How to see source Rd files from the html help pages for R functions

[Nipesh Bajaj]

Hello again, I am wondering wherether it is possible to get the source
Rd file, looking at the html help page, for any r function. I am
fighting hard to put few mathematical expressions in my help files for
my custom package. Therefore I would like to learn from some existing
html help pages how to put those expressions.

Any help will be highly appreciated.

Thanks,