Here are two more documents I have found that may be useful:

Click here then click on Modal Harmony

This article deals with what chords should be used to accompany tunes in Ionian, Dorian, Mixolydian, and Aeolian modes.

Modes and Scales in Traditional Scottish Music

The introduction to this one is tantalizing, but it looks terribly long and complete - and its millions of examples are given in abc - so I haven't worked up the courage to study it yet. But take a look if you're studying about modes.

Marion