This is a year-day method for the `calendar_count_between()`

generic.
It counts the number of `precision`

units between `start`

and `end`

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

## Usage

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

## Arguments

- start, end
`[clock_year_day]`

A pair of year-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 an individual's age in years
x <- year_day(2001, 100)
y <- year_day(2021, c(99, 101))
calendar_count_between(x, y, "year")
#> [1] 19 20
# Or in a whole number multiple of years
calendar_count_between(x, y, "year", n = 3)
#> [1] 6 6
```