[Rd] R-exts.texi: suggestion for small change to Vignette section (PR#7323)

[Kurt Hornik]

>>>>> S J Eglen writes:

> I recently wrote a vignette, with the following at the top of the .Rnw
> file:

> %%\VignetteIndexEntry{How to use look up tables for h() functions}
> %%\VignetteDepends{sjedmin, spatstat}

> Using vExplorer() on this function, I got an error from this part of
> getVigInfo():

>     lines <- grep("^%[[:space:]]*\\\\Vignette", file)
>     if (length(lines) == 0) 
>         stop("File ", vig, " does not appear to be a vignette file, ", 
>             "no vignette metadata available.")

> The error occurs here because the grep expects only one % at the start
> of the line, whereas I had %%.  (I often use two at the start of a
> line as I'm used to the ESS/Emacs coding habits of putting ## at the
> start of a line.)  Changing %% to % solved the problem okay.  

> So, my minor suggestion to R-exts.texi, at line 1011:

> @code{\VignetteIndexEntry} statement is best placed in La at TeX{} comment,

> is that maybe it should say either:

> "in a La at TeX{} comment"

> or 

> "in a La at TeX{} comment with a single %"

> although admittedly that sounds a bit clunky!

Hmm, why not change the Sweave code to support multiple comment chars?

The code for index computations on vignettes is based on

vignetteMetaRE <- function(tag)
    paste("[[:space:]]*%+[[:space:]]*\\\\Vignette", tag,
          "\{([^}]*)\}", sep = "")

-k