# File lib/ruote/svc/dollar_sub.rb, line 92
    def literal_sub(s, fexp, wi)

      case s
        when /^\$(?:variable|var|v):([^{}\s\$]+)$/
          fexp.lookup_variable($~[1])
        when /^\$([^{}:\s\$]+)$/, /^\$(?:field|fld|f):([^{}\s\$]+)$/
          Ruote.lookup(wi['fields'], $~[1])
        else
          s
      end
    end