XML in a Nutshell, 3rd Edition

Number Functions

XPath includes a few simple numeric functions for summing groups of numbers and finding the nearest integer to a number. It doesn’t have the full power of the math libraries in Java or Fortran—for instance, there’s no square root or exponentiation function—but it’s got enough to do most of the basic math you need for XSLT or the even simpler requirements of XPointer.

The number( ) function can take any type as an argument and convert it to a number. If the argument is omitted, then it converts the context node. Booleans are converted to 1 if true and 0 if false. Strings are converted in a plausible fashion. For instance the string “7.5” will be converted to the number 7.5. The string “Fred” will be converted to NaN. Node-sets are converted to numbers by first converting them to their string value and then converting the resulting string to a number. The detailed rules are a little more complex, but as long as the object you’re converting can reasonably be interpreted as a single number, chances are the number() function will do what you expect. If the object you’re converting can’t be reasonably interpreted as a single number, then the number() function will return NaN.

The round( ) , floor( ), and ceiling( ) functions all take a single number as an argument. The floor( ) function returns the greatest integer less than or equal to its argument. The ceiling( ) function returns the smallest integer greater than or equal to its argument. The round( ) function returns ...