http://www.wowinterface.com/forums/showthread.php?t=53494

Ketho_EditBox.lua

function KethoEditBox_New()
	if KethoEditBox then
		KethoEditBox:Show()
	else
		local f = CreateFrame("Frame", "KethoEditBox", UIParent, "DialogBoxFrame")
		f:SetPoint("CENTER"); f:SetSize(600, 500)
		
		f:SetBackdrop({
			bgFile = "Interface\\DialogFrame\\UI-DialogBox-Background",
			edgeFile = "Interface\\PVPFrame\\UI-Character-PVP-Highlight", -- this one is neat
			edgeSize = 16,
			insets = { left = 8, right = 6, top = 8, bottom = 8 },
		})
		f:SetBackdropBorderColor(0, .44, .87, 0.5)
		
	---------------
	--- Movable ---
	---------------
		
		f:EnableMouse(true) -- also seems to be automatically enabled when setting the OnMouseDown script
		f:SetMovable(true); f:SetClampedToScreen(true)
		f:SetScript("OnMouseDown", function(self, button)
			if button == "LeftButton" then
				self:StartMoving()
			end
		end)
		f:SetScript("OnMouseUp", f.StopMovingOrSizing)
		
	-------------------
	--- ScrollFrame ---
	-------------------
		
		local sf = CreateFrame("ScrollFrame", "KethoEditBoxScrollFrame", KethoEditBox, "UIPanelScrollFrameTemplate")
		sf:SetPoint("LEFT", 16, 0)
		sf:SetPoint("RIGHT", -32, 0)
		sf:SetPoint("TOP", 0, -16)
		sf:SetPoint("BOTTOM", KethoEditBoxButton, "TOP", 0, 0)
		
	---------------
	--- EditBox ---
	---------------
		
		local eb = CreateFrame("EditBox", "KethoEditBoxEditBox", KethoEditBoxScrollFrame)
		eb:SetSize(sf:GetSize()) -- seems inheriting the points won't automatically set the width/size
		
		eb:SetMultiLine(true) -- will be laggy with thousands of lines/text
		eb:GetRegions():SetNonSpaceWrap(false) -- fix lag?
		
		eb:SetFontObject("ChatFontNormal")
		eb:SetAutoFocus(false) -- make keyboard not automatically focused to this editbox
		eb:SetScript("OnEscapePressed", function(self)
			f:Hide() -- rather hide, since we only use it for copying to clipboard
		end)
		
		sf:SetScrollChild(eb)
		
	-----------------
	--- Resizable ---
	-----------------
		
		f:SetResizable(true)
		f:SetMinResize(150, 100) -- at least show the "okay" button
		
		local rb = CreateFrame("Button", "KethoEditBoxResizeButton", KethoEditBox)
		rb:SetPoint("BOTTOMRIGHT", -6, 7); rb:SetSize(16, 16)
		
		rb:SetNormalTexture("Interface\\ChatFrame\\UI-ChatIM-SizeGrabber-Up")
		rb:SetHighlightTexture("Interface\\ChatFrame\\UI-ChatIM-SizeGrabber-Highlight")
		rb:SetPushedTexture("Interface\\ChatFrame\\UI-ChatIM-SizeGrabber-Down")
		
		rb:SetScript("OnMouseDown", function(self, button)
			if button == "LeftButton" then
				f:StartSizing("BOTTOMRIGHT")
				self:GetHighlightTexture():Hide() -- we only want to see the PushedTexture now 
			end
		end)
		rb:SetScript("OnMouseUp", function(self, button)
			f:StopMovingOrSizing()
			self:GetHighlightTexture():Show()
			eb:SetWidth(sf:GetWidth()) -- update editbox to the new scrollframe width
		end)
		f:Show()
	end
end