[boost] [string_algo] trimming a range

According to the documentation http://www.boost.org/doc/html/trim_copy.html one can not pass a range to boost::algorithm::trim_copy, and the sequence requirements must be met for the first parameter. Considering how trim_copy_if is implemented, one can use it with ranges (for example, with boost::iterator_range). Is there any reason the documentation requires one to pass a sequence? Is there any safe and documented way to trim a range, i.e. having two iterators (begin, end) get a trimmed subrange? Thanks, Valentin