Source

File: wp-includes/Requests/IRI.php

protected function remove_dot_segments($input) {
		$output = '';
		while (strpos($input, './') !== false || strpos($input, '/.') !== false || $input === '.' || $input === '..') {
			// A: If the input buffer begins with a prefix of "../" or "./",
			// then remove that prefix from the input buffer; otherwise,
			if (strpos($input, '../') === 0) {
				$input = substr($input, 3);
			}
			elseif (strpos($input, './') === 0) {
				$input = substr($input, 2);
			}
			// B: if the input buffer begins with a prefix of "/./" or "/.",
			// where "." is a complete path segment, then replace that prefix
			// with "/" in the input buffer; otherwise,
			elseif (strpos($input, '/./') === 0) {
				$input = substr($input, 2);
			}
			elseif ($input === '/.') {
				$input = '/';
			}
			// C: if the input buffer begins with a prefix of "/../" or "/..",
			// where ".." is a complete path segment, then replace that prefix
			// with "/" in the input buffer and remove the last segment and its
			// preceding "/" (if any) from the output buffer; otherwise,
			elseif (strpos($input, '/../') === 0) {
				$input = substr($input, 3);
				$output = substr_replace($output, '', strrpos($output, '/'));
			}
			elseif ($input === '/..') {
				$input = '/';
				$output = substr_replace($output, '', strrpos($output, '/'));
			}
			// D: if the input buffer consists only of "." or "..", then remove
			// that from the input buffer; otherwise,
			elseif ($input === '.' || $input === '..') {
				$input = '';
			}
			// E: move the first path segment in the input buffer to the end of
			// the output buffer, including the initial "/" character (if any)
			// and any subsequent characters up to, but not including, the next
			// "/" character or the end of the input buffer
			elseif (($pos = strpos($input, '/', 1)) !== false) {
				$output .= substr($input, 0, $pos);
				$input = substr_replace($input, '', 0, $pos);
			}
			else {
				$output .= $input;
				$input = '';
			}
		}
		return $output . $input;
	}