Each part of the string surrounded by "#{}"
is extracted, evaluated
as R code in the specified environment, and then its value is substituted
back into the string. The literal string "#{}"
can be obtained by
escaping the hash character, viz. "\\#{}"
. The block may contain
multiple R expressions, separated by semicolons, but may not contain
additional braces. Its value will be coerced to character mode, and if the
result has multiple elements then the source string will be duplicated.