system/HTTP/Message.php
protected function getHeaderName(string $name): string
	{
		$lower_name = strtolower($name);

		return $this->headerMap[$lower_name] ?? $name;
	}
protected function getHeaderName(string $name): string
	{
		$lower_name = strtolower($name);

		return $this->headerMap[$lower_name] ?? $name;
	}
Takes a header name in any case, and returns the
normal-case version of the header.

@param string $name

@return string