Preferences Mouse Behavior

Mouse editing behavior
Clicking on an envelope segment	Click on the down arrow to select the action that will occur when clicking on a segment of an Envelope. Holding down the Shift key while clicking will force the alternative behavior.
Control+drag media items	Click the down arrow to select the action that will occur when dragging a media Item while holding the Ctrl key.
Doubleclicking items	Click the down arrow to select the action that will occur when double-clicking on a media Item. Holding down the Shift key while double-clicking will select the alternative behaviour.
Mousewheel targets	Click the down arrow to select the focus of mousewheel movements.
Ignore mousewheel on faders
When clicking/dragging in a loop selection, move loop selection	By default, REAPER will start drawing a new loop selection if you click and drag in an existing loop selection. Selecting this check box will change the behavior so that you can slide the position of a loop selection by clicking and dragging inside the selection. Holding down the Shift key will force the default behavior.
Mousewheel modifier keys for main view All the below have these options:
Vertical Zoom	Choose which key is the modifier!
Horizontal Zoom	Choose which key is the modifier!
Vertical Scroll	Choose which key is the modifier!
Horizontal Scroll	Choose which key is the modifier!