Filtering posts by any property

[braco]

Allow Filtering by Custom Field | WP ACF API

https://joshuabedford.com/blog/allow-filtering-by-custom-field-wp-acf-api

Am I not seeing something obvious, why isn't this part of the core package?

[shershen08]

thanks for the provided example - https://joshuabedford.com/blog/allow-filtering-by-custom-field-wp-acf-api
where should I place such a file for enabling filtering in my WP installation ?