This is no longer a part of the World of Warcraft API. It was replaced with GameTooltip:SetUnitBuff. It was removed in patch 3.0.2.

Sets a GameTooltip to a player buff of the type last used in GetPlayerBuff.

GameTooltip:SetPlayerBuff(buffIndex)

Arguments Edit

buffIndex 

Number - The index of the buff to set in the game tooltip (affected by the filter used in GetPlayerBuff)

Returns Edit

nil

Example Edit

local buffIndex, untilCancelled = GetPlayerBuff(1, "HARMFUL");
GameTooltip:SetPlayerBuff(buffIndex);

Result

The GameTooltip is set to the first harmful buff.

Details Edit

It will use whatever the last type of buff you specified in GetPlayerBuff was, hence the reason you should specify GetPlayerBuff right before you call SetPlayerBuff.

Options for the GetPlayerBuff filter are : HELPFUL|HARMFUL|PASSIVE