wp-includes/class-wp-block-processor.php:1381Indicates if the last attempt to parse a block’s JSON attributes failed.
int public function get_last_json_error(): int { return $this->last_json_error; }Introduced in 6.9.0. Unchanged from 6.9.7 through 7.1.0.
Signature, return type and hooks compared across 3 parsed releases.
src/wp-includes/class-wp-block-processor.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.