in src/main/java/org/apache/sling/feature/extension/unpack/Unpack.java [238:245]
private String relativize(List<String> roots, String path) {
for (String root : roots) {
if (("/" + path).startsWith(root)) {
return path.substring(root.length() -1);
}
}
throw new IllegalStateException("Can't find a root for: " + path);
}