Source

File: wp-includes/post.php

function wp_set_post_terms( $post_id = 0, $tags = '', $taxonomy = 'post_tag', $append = false ) {
	$post_id = (int) $post_id;

	if ( ! $post_id ) {
		return false;
	}

	if ( empty( $tags ) ) {
		$tags = array();
	}

	if ( ! is_array( $tags ) ) {
		$comma = _x( ',', 'tag delimiter' );
		if ( ',' !== $comma ) {
			$tags = str_replace( $comma, ',', $tags );
		}
		$tags = explode( ',', trim( $tags, " \n\t\r\0\x0B," ) );
	}

	/*
	 * Hierarchical taxonomies must always pass IDs rather than names so that
	 * children with the same names but different parents aren't confused.
	 */
	if ( is_taxonomy_hierarchical( $taxonomy ) ) {
		$tags = array_unique( array_map( 'intval', $tags ) );
	}

	return wp_set_object_terms( $post_id, $tags, $taxonomy, $append );
}