
1.) Add a function to your AddOn that will handle the content you wish to add
    to a Link Wrangler Tooltip. It must adhere to the following prototype, but
    can have any name you wish (i.e. only the function arguments are required):

function MyAddOn_AddStuff(frame,link)
-- Your code here
frame:AddLine(link);
frame:AddLine("test 1a\nnew lines");
end

2.) Add the following code to your AddOn's OnLoad Handler:

this:RegisterEvent("VARIABLES_LOADED");

3.) Add the following code to your AddOns OnEvent handler:

if (event == "VARIABLES_LOADED") then
if (IsAddOnLoaded("Link Wrangler") ~= nil) then
LINK_WRANGLER_CALLER["MyAddOnName"] = "MyAddOn_AddStuff";
end
end

Your function needs to be a string and not the function itself (for error 
checking). It will not work if you have:
LINK_WRANGLER_CALLER["MyAddOnName"] = MyAddOn_AddStuff; -> it must be 
LINK_WRANGLER_CALLER["MyAddOnName"] = "MyAddOn_AddStuff";

The index of the your AddOn's function should be the name of your AddOn.

Once your function appears in the LINK_WRANGLER_CALLER table, it will be called
when any Link Wrangler window is opened.
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