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findcontour points order

Hi, I'm using this function:

cv::findContours(frame, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);

Debugging my application I noticed that for any contour detected, the first point, contour[0], always is the topmost point, with the lowest y value. Is that really true? I didn't find any reference in the documentation about the point order. Is this a reliable way to find the topmost point of a contour?