in src/main/java/org/apache/sling/scripting/thymeleaf/internal/SlingTemplateResource.java [68:75]
public ITemplateResource relative(final String relativeLocation) {
final PathBuilder pathBuilder = new PathBuilder(resource.getPath());
final String path = pathBuilder.append("..").append(relativeLocation).toString();
final ResourceResolver resourceResolver = resource.getResourceResolver();
final Resource relative = resourceResolver.getResource(path);
// final Resource relative = resource.getParent().getChild(relativeLocation);
return new SlingTemplateResource(relative);
}