substring-before Function
Returns the substring of the first argument string that precedes the first occurrence of the second argument string in the first argument string, or the empty string if the first argument string does not contain the second argument string.
string substring-before(string, string)
Remarks
If an argument is not of type string, it is first converted to a string and then evaluated.
The following function call returns "1999":
substring-before("1999/04/01","/")
The following function call returns an empty string "":
substring-before("1999/04/01","2")
See Also
Data Types in Schemas | XDR Schema Data Types Reference | XML Data Types Reference