That General Convention’s constitution and canons place in a primary way the clergy under the Scripture as “God’s Word.”
That the Book of Common Prayer, which General Convention guards and potentially amends, binds the Episcopal Church to the “essential” doctrine, discipline, and worship (though not the sanctions) of another church, that is, of the Church of England (BCP, p.11).
That the same Book of Common Prayer binds the Episcopal Church’s bishops to other churches and bishops and to their teaching and discipline from different ages and places, not even necessarily Anglican ones (cf. p. 510 on “recognizability” and p. 517 on the apostolic and universal “heritage” shared by Episcopal bishops and to which they are accountable).
That these bonds themselves, variously linked to elements of the Scriptures and their teaching — according to what the prayers of the BCP teach (e.g., pp. 215, 218, 236, 240, 243) — are viewed as divinely imposed and upheld.

None of these points simply answers the question of General Convention’s authority. But taken together — along with other elements not mentioned here — they indicate a shape and limit to that authority: the Convention and the Episcopal Church it somehow serves are under the authority of the Scriptures, are properly guided by the teaching of bishops subjected to a larger worldwide tradition, are nourished by clergy similarly ordered in their teaching and example, and are embodied and extended by a people so nourished whose scripturally informed lives mold the whole.

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