wp-includes/SimplePie/src/XML/Declaration/Parser.php:147Advance past any whitespace
int public function skip_whitespace() { $whitespace = strspn($this->data, "\x09\x0A\x0D\x20", $this->position); $this->position += $whitespace; return $whitespace; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/SimplePie/src/XML/Declaration/Parser.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.