def find_within(tags, span, pointer)
      puts "--#{span}" if Chronic.debug
      return span if tags.empty?

      head = tags.shift
      head.start = (pointer == :future ? span.begin : span.end)
      h = head.this(:none)

      if span.cover?(h.begin) || span.cover?(h.end)
        find_within(tags, h, pointer)
      end
    end
def find_within(tags, span, pointer)
      puts "--#{span}" if Chronic.debug
      return span if tags.empty?

      head = tags.shift
      head.start = (pointer == :future ? span.begin : span.end)
      h = head.this(:none)

      if span.cover?(h.begin) || span.cover?(h.end)
        find_within(tags, h, pointer)
      end
    end
Recursively finds repeaters within other repeaters.
 Returns a Span representing the innermost time span
 or nil if no repeater union could be found