@substr()

This takes two or three arguments and extracts substrings from the first
argument based on the remaining one(s).

Usage (3 arguments):
@substr( "alpacas are funny", "8", "3" )

Result is "are".  If the second argument is negative, the substring starts
that far from the end of the string instead.  If the third argument is
negative, the length is calculated to leave that many characters off the
end of the string.

Usage (2 arguments):
@substr( "monkeys are funnier", "12" )

Result is "funnier".  Like the 3-argument form, if the second argument is
negative, the substring starts that far from the end of the string
instead.