
How do I add a validation to make sure the date string being passed to the method is in the ffg. format:
```'YYYY-MM-DD'
```
if it's not, method should raise some sort of error
How is arc defined in TikZ?

TikZ is a powerful drawing package for LaTeX that uses MetaPost language for defining custom shapes and drawing paths. In TikZ, you can define an arc by using the arc command. Here's a basic syntax:

```latex
\draw [<options>] (<start point>) -- (<control point 1>) -| (<control point 2>) |- (<end point>) [<angle>] ;
```

To define an arc specifically, you can use the `arc` command in MetaPost language. Its syntax is as follows
?
When working with methods that accept date strings in the format you specified, you can use a validation in your method to check if the format is correct or not before processing the date string. Here's an example of how you can implement this in Ruby:
```ruby
def process_date(date_string)
  if !date_string.match(/^\d{4}-\d{2}-\d{2}$/)
    raise ArgumentError.new("Invalid date format. Date string must be in the format 'YYYY-MM-DD'")
  end
  # Process the