First you need a mouse with a wheel.
Then in RDx it's Window / Preferences / LPEX Editor / User Mouse Actions.
In here, put wheelDown as the mouse action, select "showAll" from the Action
dropdown list, and click Set.
Then put wheelUp as the mouse action, select "filterSelection" from the
Action dropdown list, and click Set.
Click OK and then, when editing, you can proceed as I described in the
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