etc... is whatever you want it to be (Lr will not parse).
Example from cookmarks plugin:
|URLHandler = "urlHandler.lua",|
URLHandler = function(url)
if url:sub( 1, 1 ) == '"' then -- double-quote wrapped format.
cookmarks:urlHandler( url:sub( 2, -2 ) ) -- strip double-quotes.
cookmarks:urlHandler( url )
Note: you have to be prepared for double-quote wrapping, and not, unless you don't care whether it's reliable - dunno details..