This is an iso-year-week-day method for the `calendar_count_between()`

generic. It counts the number of `precision`

units between `start`

and `end`

(i.e., the number of ISO years).

## Usage

```
# S3 method for clock_iso_year_week_day
calendar_count_between(start, end, precision, ..., n = 1L)
```

## Arguments

- start, end
`[clock_iso_year_week_day]`

A pair of iso-year-week-day vectors. These will be recycled to their common size.

- precision
`[character(1)]`

One of:

`"year"`

- ...
These dots are for future extensions and must be empty.

- n
`[positive integer(1)]`

A single positive integer specifying a multiple of

`precision`

to use.

## Examples

```
# Compute the number of whole ISO years between two dates
x <- iso_year_week_day(2001, 1, 2)
y <- iso_year_week_day(2021, 1, c(1, 3))
calendar_count_between(x, y, "year")
#> [1] 19 20
```