+-,---------+
     V           |
>>-[---+-------+-+-]=value-------------------------------------><
       +-index-+

Makes the value a member item of the stem collection and associates it with the specified index. The final index is derived by concatenation each of the index arguments together with a "." separator. If you specify no index arguments, a new default stem value is assigned. Assigning a new default value will re-initialize the stem and remove all existing assigned indexes.