Source

File: wp-includes/class-wp-term-query.php

public function parse_query( $query = '' ) {
		if ( empty( $query ) ) {
			$query = $this->query_vars;
		}

		$taxonomies = isset( $query['taxonomy'] ) ? (array) $query['taxonomy'] : null;

		/**
		 * Filters the terms query default arguments.
		 *
		 * Use {@see 'get_terms_args'} to filter the passed arguments.
		 *
		 * @since 4.4.0
		 *
		 * @param array    $defaults   An array of default get_terms() arguments.
		 * @param string[] $taxonomies An array of taxonomy names.
		 */
		$this->query_var_defaults = apply_filters( 'get_terms_defaults', $this->query_var_defaults, $taxonomies );

		$query = wp_parse_args( $query, $this->query_var_defaults );

		$query['number'] = absint( $query['number'] );
		$query['offset'] = absint( $query['offset'] );

		// 'parent' overrides 'child_of'.
		if ( 0 < intval( $query['parent'] ) ) {
			$query['child_of'] = false;
		}

		if ( 'all' === $query['get'] ) {
			$query['childless']    = false;
			$query['child_of']     = 0;
			$query['hide_empty']   = 0;
			$query['hierarchical'] = false;
			$query['pad_counts']   = false;
		}

		$query['taxonomy'] = $taxonomies;

		$this->query_vars = $query;

		/**
		 * Fires after term query vars have been parsed.
		 *
		 * @since 4.6.0
		 *
		 * @param WP_Term_Query $this Current instance of WP_Term_Query.
		 */
		do_action( 'parse_term_query', $this );
	}