法華玄義釋籤 3.28

3.28

言釋成者，以義同故引來相成，令論意可識，非謂將經解釋論也。況復此是申經別論，於理無傷。

When it speaks of confirming through explanation, because their meanings are identical, they are cited to mutually confirm each other and make the intent of the treatises recognizable; it does not mean taking sūtras to comment on treatises. Moreover, this is a separate treatise that expounds the sūtras, so there is no harm to principle.