This expression uses a quantifier
? to optionally
match things. Specifically, the question mark makes the preceding token in
the regular expression optional.
rx_maybe(.data = NULL, value)
Expression to append, typically pulled from the pipe
Expression to optionally match
rx_maybe(value = "abc")#>  "(abc)?"# create expression x <- rx() %>% rx_start_of_line() %>% rx_maybe("abc") %>% rx_end_of_line(enable = FALSE) grepl(x, "xyz") # should be true#>  TRUE