The Higher-Order built-in functions are XQuery functions to support
higher-order functions, and are part of the XQuery 3.0 working draft.
They are defined in
XPath and
XQuery Functions and Operators 3.0.
Processes the supplied sequence from left to right, applying the supplied function repeatedly to each item in turn, together with an accumulated result value.
Processes the supplied sequence from right to left, applying the supplied function repeatedly to each item in turn, together with an accumulated result value.
Applies the function item $function to successive pairs of items taken one from $seq1 and one from $seq2, returning the concatenation of the resulting sequences in order.