ORA-FO-INTEGERPARAMS 7.4.6 fn:substring

*Functions and Operators, Section 7.4.6 fn:substring* has a $startingLoc 
parameter that is an xs:double. Why isn't this an xs:integer ?

cf 7.4.15 fn:string-pad where the $padCount parameter is xs:integer.
cf 15.1.14 fn:subsequence where $startingLoc is double
cf 15.1.12 fn:insert-before, 15.1.13 fn:remove where $position is integer

If this is because of backwards-compatibility, an explanatory note to 
that effect would be helpful.