In 8.7.4 "The DragEvent interface",
in the algorithm for 'fire a DND event',
step 4 says:
    ... and to a value based on the effectAllowed attribute's value
    and to the drag-and-drop source, as given by the following table, ...

Grammatically, the second "and to" would seem to be parallel to the first,
but the phrase doesn't make sense if you try to read it that way.

Delete the second "to", I think.