{category1 
    {subcategory1
        {1a b2 c3 d4}}
    {subcategory2 
        {1a 2b 3c 4d}}}
{category2
    {subcategoryA 
        {a1 b2 c3 d4}}
    {subcategoryB
        {1a 2b 3c 4d}}}
{audio
    {math
        {+~ /~ *~ pow}}}