# File lib/ruote/storage/base.rb, line 144
    def expression_wfids(opts)

      wfids = ids('expressions').collect { |fei| fei.split('!').last }.uniq.sort

      wfids = wfids.reverse if opts[:descending]

      skip = opts[:skip] || 0
      limit = opts[:limit] || wfids.length

      wfids[skip, limit]
    end