isValidPath static method
Must start with /, not end with /, no spaces/backslashes. Empty is
allowed (level2's default path).
Implementation
static bool isValidPath(String path) {
if (path.isEmpty) return true;
return path.startsWith('/') &&
!path.endsWith('/') &&
!path.contains(' ') &&
!path.contains(r'\') &&
path.length > 1;
}