
The function returns the average of all values in all its arguments,
For each node in every argument node-set, it converts the string-value of the node to a number and adds the result to the sum.
If some arguments are not node-sets, they are converted to numbers first and added to the sum.
Then sum is divided by number of values added and the result is returned.

This function is not a part of XPATH 1.0 standard library.
