What is the ruling when dark blood (aswad) appears between two periods of red blood (ahmar) and this total period is less than the maximum duration of menstruation?

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If dark blood appears between two instances of red blood, or red blood appears between two instances of dark blood, and the total duration falls short of the maximum duration of menstruation, the entirety is considered menstruation if this pattern repeats. This is because the red blood is considered more similar to menstrual blood than to a period of purity. If the dark blood alone is sufficient to constitute a minimum period of menstruation, and the red blood does not exceed the maximum period, the dark blood is deemed menstruation, and the red blood is considered irregular bleeding (istihada). The dark blood aggregates with other dark blood, thus constituting the full menstrual period. This applies regardless of whether the dark blood is little or much, provided its total duration, when combined with other dark blood, meets the minimum duration of menstruation but does not exceed the maximum, and the time between the ends of these bleeding segments does not surpass the maximum duration of purity.