capture: Capture a token, or not
In richierocks/rebus.base: Core Functionality for the 'rebus' Package

Description Usage Arguments Value References See Also Examples

Create a token to capture or not.

capture(x)

group(x)

token(x)

engroup(x, capture)

`x`	A character vector.
`capture`	Logical If `TRUE`, call `capture`; if `FALSE`, call `group`.

A character vector representing part or all of a regular expression.

http://www.regular-expressions.info/brackets.html

or for more examples

x <- "foo"
capture(x)
group(x)

# Usage
# capture is good with match functions
(rx_price <- capture(digit(1, Inf) %R% DOT %R% digit(2)))
(rx_quantity <- capture(digit(1, Inf)))
(rx_all <- DOLLAR %R% rx_price %R% " for " %R% rx_quantity)
stringi::stri_match_first_regex("The price was $123.99 for 12.", rx_all)

# group is mostly used with alternation.  See ?or.
(rx_spread <- group("peanut butter" %|% "jam" %|% "marmalade"))
stringi::stri_extract_all_regex(
  "You can have peanut butter, jam, or marmalade on your toast.",
  rx_spread
)