clarify documentation of `delim` argument in read_delim

[EmilHvitfeldt]

I will preface this with saying that I don't know if this is a good issue, and that I don't have a good solution.

When reading the documentation for read_delim(), the delim argument states:

Single character used to separate fields within a record.

for a second, I thought that you could only use single character strings as delim but with some testing it found that it accept a length 1 character vector with any number of characters. I know this is kinda messy, but I wonder if the wording could be clarified

library(readr)
temp_f <- tempfile()
write_lines(
  c("4-,45-,564-,4",
    "4-,42-,534-,3",
    "4-,45-,564-,1"),
  temp_f
)

read_delim(temp_f, delim = "-,", col_names = FALSE)
#> Rows: 3 Columns: 4
#> ── Column specification ────────────────────────────────────────────────────────
#> Delimiter: "-,"
#> dbl (4): X1, X2, X3, X4
#> 
#> ℹ Use `spec()` to retrieve the full column specification for this data.
#> ℹ Specify the column types or set `show_col_types = FALSE` to quiet this message.
#> # A tibble: 3 × 4
#>      X1    X2    X3    X4
#>   <dbl> <dbl> <dbl> <dbl>
#> 1     4    45   564     4
#> 2     4    42   534     3
#> 3     4    45   564     1

^{Created on 2022-12-04 with reprex v2.0.2}

[Henning-Lenz]

I also initially understood, that the delim argument will take only one character for separating the contents, but tested it (accidentally) to be also working with e.g. " > ".

Also #802 states that multiple characters as delim are officially OK, but the help does not say so, yet.