1  <doc>
 2    <!-- at least one present -->
 3    <z-o>
 4      <b/>
 5    </z-o>
 6    <o-o>
 7      <c/>
 8    </o-o>
 9    <z-u>
10      <d/>
11    </z-u>
12    <o-u>
13      <e/>
14    </o-u>
15    <z-3>
16      <f/>
17    </z-3>
18    <o-3>
19      <g/>
20    </o-3>
21    <!-- more than one present when allowed -->
22    <z-o>
23      <b/>
24    </z-o>
25    <o-o>
26      <c/>
27    </o-o>
28    <z-u>
29      <d/>
30      <d/>
31      <d/>
32    </z-u>
33    <o-u>
34      <e/>
35      <e/>
36      <e/>
37    </o-u>
38    <z-3>
39      <f/>
40      <f/>
41      <f/>
42    </z-3>
43    <o-3>
44      <g/>
45      <g/>
46      <g/>
47    </o-3>
48    <!-- min 0 are not present -->
49    <z-o/>
50    <o-o>
51      <c/>
52    </o-o>
53    <z-u/>
54    <o-u>
55      <e/>
56    </o-u>
57    <z-3/>
58    <o-3>
59      <g/>
60    </o-3>
61  </doc>