[Tuhljin]

"self" is implied as the first argument if the function is defined like so:

function MyTable:PrintNameAndNumber(num)
  print(self.name, num)
end

Notice the colon (":").

It's also implied when used in the XML like this:

<OnEnter>
  GameTooltip:SetOwner(self, "ANCHOR_RIGHT");
  GameTooltip:AddLine(self.date, 1, 1, 1);
  GameTooltip:Show();
</OnEnter>

However, in a case like the below, self isn't implied so you'd have to put it in yourself:

MyFrame:RegisterEvent("ZONE_CHANGED_NEW_AREA")
MyFrame:SetScript("OnEvent", function(self)
  print(self.name)
end)

See: http://lua-users.org/wiki/ObjectOrientationTutorial