
The function converts all its arguments into strings using the same rules as XPATH function string(),
then it performs concatenation and returns the resulting string.

XPATH 1.0 standard states that concat() function must have at least 2 arguments,
but in Virtuoso XPATH this restriction is eliminated.
concat() may be called without arguments (it will return an empty string)
or with one argument (it will work like string() function).
This may be useful if the text of XPATH expression must be generated by
an application.
