wp-includes/SimplePie/src/Parser.php:240 public function get_error_string() { return $this->error_string; }One change between 6.7.7 and 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
none to string.verified against sourcesrc/wp-includes/SimplePie/src/Parser.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.