WordPress at a glance
function is not described

_wp_preview_terms_filter() WP 3.6.0

Filters terms lookup to set the post format.

This is an internal function for using it by WP core itself. It's not recommended to use this function in your code.

No Hooks.

Return

Array. Null. Nothing.

Usage

_wp_preview_terms_filter( $terms, $post_id, $taxonomy );
$terms(array) (required)
-
$post_id(int) (required)
-
$taxonomy(string) (required)
-

Changelog

Since 3.6.0 Introduced.

Code of _wp_preview_terms_filter() WP 5.7.1

<?php
function _wp_preview_terms_filter( $terms, $post_id, $taxonomy ) {
	$post = get_post();
	if ( ! $post ) {
		return $terms;
	}

	if ( empty( $_REQUEST['post_format'] ) || $post->ID != $post_id
		|| 'post_format' !== $taxonomy || 'revision' === $post->post_type
	) {
		return $terms;
	}

	if ( 'standard' === $_REQUEST['post_format'] ) {
		$terms = array();
	} else {
		$term = get_term_by( 'slug', 'post-format-' . sanitize_key( $_REQUEST['post_format'] ), 'post_format' );
		if ( $term ) {
			$terms = array( $term ); // Can only have one post format.
		}
	}

	return $terms;
}