WordPress at a glance
function is not described

WP_Tax_Query::is_first_order_clause() protected WP 4.1.0

Determine whether a clause is first-order.

A "first-order" clause is one that contains any of the first-order clause keys ('terms', 'taxonomy', 'include_children', 'field', 'operator'). An empty clause also counts as a first-order clause, for backward compatibility. Any clause that doesn't meet this is determined, by process of elimination, to be a higher-order query.

{} It's a method of the class: WP_Tax_Query{}

No Hooks.

Return

true|false. Whether the query clause is a first-order clause.

Usage

$result = WP_Tax_Query::is_first_order_clause( $query );
$query(array) (required)
Tax query arguments.

Changelog

Since 4.1.0 Introduced.

Code of WP_Tax_Query::is_first_order_clause() WP 5.7

<?php
protected static function is_first_order_clause( $query ) {
	return is_array( $query ) && ( empty( $query ) || array_key_exists( 'terms', $query ) || array_key_exists( 'taxonomy', $query ) || array_key_exists( 'include_children', $query ) || array_key_exists( 'field', $query ) || array_key_exists( 'operator', $query ) );
}