This allows you to specify arbitary roots of an expression. The radix comes first, and is separated from the radicand by the <OF> tag.
none
<ROOT> is legal within:
<ABOVE>, <BAR>, <BELOW>, <BOX>, <BT>, <DDOT>,
<DOT>, <HAT>, <ITEM>, <MATH>, <OF>, <ROOT>, <SQRT>,
<T>, <TILDE>, <VEC>
The following markup can be used within <ROOT>
<ABOVE>, <ARRAY>, <B>, <BAR>, <BELOW>, <BOX>,
<BT>, <DDOT>, <DOT>, <HAT>, <OF>, <ROOT>, <SQRT>,
<SUB>, <SUP>, <T>, <TILDE>, <VEC>
<MATH><ROOT>3<OF>1 + x</ROOT></MATH>