code: public Context createChild(String name) {
          Preconditions.checkArgument(name.indexOf('/') == -1, "name must not contain a slash");
          Preconditions.checkArgument(!children.containsKey(name), "child with name '%s' already exists", name);
          Preconditions.checkArgument(!values.containsKey(name), "name identifies a key-value pair",
                  "createChild operation not allowed");
          Context child = new Context();
          children.put(name, child);
          return child;
      }
docs: Create a new child {@code Context}. The name must not contain any slashes ({@code '/'}).
  
  @throws IllegalArgumentException if a child or key-value pair with the given @{code name} exists.