math:max() returns the maximum value of a node-set.
To compute the maximum value of the node-set, the node set is sorted into descending order as it would be using
xsl:sort() with a data type of
number. The maximum value is then the first node in the sorted list, converted into a number.
The node-set whose highest value is to be returned.
A result tree fragment representing the highest valued node's numeric value as a string.