Very handy if you don't want your units to run through dangerous areas full of enemies, but keep their distance.

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Also works with Right Mouse Drag, to draw a line, just like the Move Line Drag command.

You can use Fight with construction and resurrect units as well.

Fight

Combat units = Move and stop to attack when enemies are within firing range
Construction units = Move and stop to Repair or Assist everything on the movement path
Resurrect units = Move and stop to Repair or Reclaim everything on the movement path

ALT + Fight

Resurrect units = Move and stop to Repair or Resurrect everything on the movement path

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