From Riftui Wiki
UIParent is a global variable given to an Addon and is a reference to the Addon's Layout. It may be use in a frame's SetPoint method, however, the only frame that is able to be attached to it is a context frame. See Layout for more information on available methods.
-- Create a context to place frames on -- local context = UI.CreateContext("SampleContext") -- Sample frame with SetPoint -- local sample = UI.CreateFrame("Frame", "SampleFrame", context) -- Attach the frame to the top left corner of the screen -- sample:SetPoint("TOPLEFT", UIParent, "TOPLEFT")