[SDPhantom]

I have this running in my development addon.

local tostring=tostring;
 
local ProxyLookup={};
local ProxyMeta={__index={
    Print=function(self,...)
        local frame=ProxyLookup[self];
        if frame then
            local msg="";
            for i=1,select("#",...) do msg=(msg~="" and msg.." " or "")..tostring(select(i,...)); end
            frame:AddMessage(msg);
            if not frame:IsShown() then FCF_StartAlertFlash(frame); end
        end
    end;
 
    Show=function(self)
        local frame=ProxyLookup[self];
        if frame then
            local tab=_G[frame:GetName().."Tab"];
            if not tab:IsShown() then
                frame:Show();
                tab:Show();
                FCF_DockFrame(frame,#FCFDock_GetChatFrames(GENERAL_CHAT_DOCK)+1,nil);
            end
        end
    end;
    Hide=function(self)
        local frame=ProxyLookup[self];
        if frame then
            local tab=_G[frame:GetName().."Tab"];
            if tab:IsShown() then-- Mimic FCF_Close(), but don't release frame
                FCF_UnDockFrame(frame);
                HideUIPanel(frame);
                tab:Hide();
                FCF_FlagMinimizedPositionReset(frame);
                if frame.minFrame and frame.minFrame:IsShown() then frame.minFrame:Hide(); end
            end
        end
    end;
 
    SetShown=function(self,show)
        local frame=ProxyLookup[self];
        if frame then self[show and "Show" or "Hide"](self); end
    end;
    IsShown=function()
        local frame=ProxyLookup[self];
        if frame then return _G[frame:GetName().."Tab"]:IsShown(); end
    end;
 
    Close=function(self)
        local frame=ProxyLookup[self];
        if frame then FCF_Close(frame); end
    end;
}};
 
hooksecurefunc("FCF_Close",function(frame,other)
    frame=other or frame;
    local proxy=ProxyLookup[frame];
    if proxy then ProxyLookup[proxy],ProxyLookup[frame]=nil,nil; end
end);
 
function CreateDebugMessageFrame(name,r,g,b,a)
    local frame=FCF_OpenTemporaryWindow("SYSTEM");
    ChatFrame_RemoveMessageGroup(frame,"SYSTEM");
 
    FCF_SetWindowName(frame,name,true);
    if r and g and b then FCF_SetWindowColor(frame,r,g,b,true); end
    if a then FCF_SetWindowAlpha(frame,a,true); end
 
    local proxy=setmetatable({},ProxyMeta);
    ProxyLookup[proxy],ProxyLookup[frame]=frame,proxy;
    return proxy;
end
 
function CreateDebugPrint(...)
    local frame=CreateDebugMessageFrame(...);
    return function(...) return frame:Print(...); end,frame;
end

Two global functions are available in this API, CreateDebugMessageFrame() and CreateDebugPrint(). The first returns a proxy object that can be used to print to and show/hide the frame as well as release the chat window to the default UI (closing it). The second quickly creates the frame and returns just the print handler function you can call to print to the window.