Source

File: wp-includes/Requests/IRI.php

protected function set_host($ihost) {
		if ($ihost === null) {
			$this->ihost = null;
			return true;
		}
		if (substr($ihost, 0, 1) === '[' && substr($ihost, -1) === ']') {
			if (Requests_IPv6::check_ipv6(substr($ihost, 1, -1))) {
				$this->ihost = '[' . Requests_IPv6::compress(substr($ihost, 1, -1)) . ']';
			}
			else {
				$this->ihost = null;
				return false;
			}
		}
		else {
			$ihost = $this->replace_invalid_with_pct_encoding($ihost, '!$&\'()*+,;=');

			// Lowercase, but ignore pct-encoded sections (as they should
			// remain uppercase). This must be done after the previous step
			// as that can add unescaped characters.
			$position = 0;
			$strlen = strlen($ihost);
			while (($position += strcspn($ihost, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ%', $position)) < $strlen) {
				if ($ihost[$position] === '%') {
					$position += 3;
				}
				else {
					$ihost[$position] = strtolower($ihost[$position]);
					$position++;
				}
			}

			$this->ihost = $ihost;
		}

		$this->scheme_normalization();

		return true;
	}