API UnitIsVisible

Returns true if the game client can see the unit.
 visible = UnitIsVisible(unit)
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;Arguments
:(String unit)
:;unit:UnitId of the unit
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;Returns
:;visible: - 1 if client can see unit, nil if not
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;Details
:The game client can see objects (including units) that the server has told it to load (and has not yet told it to unload). The server provides objects in a 100-yard radius, but seems to load them in batches.
:This does not check for line-of-sight, only for game client visibility.