This is a year-month-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 or months).

## Usage

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

## Arguments

- start, end
`[clock_year_month_day]`

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

- precision
`[character(1)]`

One of:

`"year"`

`"quarter"`

`"month"`

- ...
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_month_day(2001, 2, 4)
today <- year_month_day(2021, 11, 30)
calendar_count_between(x, today, "year")
#> [1] 20
# Compute the number of months between two dates, taking
# into account the day of the month and time of day
x <- year_month_day(2000, 4, 2, 5)
y <- year_month_day(2000, 7, c(1, 2, 2), c(3, 4, 6))
calendar_count_between(x, y, "month")
#> [1] 2 2 3
```