This replaces any character in expression1 that also occurs in expression2 with the corresponding character from expression3. The identifier is unique not only within the document, but within all documents opened during the run. There are some constructs that are specifically numeric expressions, but in addition any string whose value is convertible to a number can be used as a number. A boolean is converted to a number by treating false as 0 and true as 1. This performs an explicit type conversion to a number, which will always give the same result as the implicit conversion described above.
Explicit conversion can be useful when assigning a value to a variable.
It is also useful when creating an qualifier in a nodeset expression, since the meaning of a numeric qualifier is different from a boolean one. This returns the number of nodes in the node-set. This converts the value of each node in the node-set to a number, and totals the result. This returns the number of characters in the string value of expression. This performs an arithmetic operation on the two values.