[NTG-context] catch % in gsub("%", "\\letterpercent")

Dear list, I have and \xmlraw command that gives some text with percent signs. ConTeXt parses them as comments (so no output). Using Lua gsub(), I need to replace something like: string.gsub([[\xmlraw{#1}{.}]], "%", "\\letterpercent") How do I need to invoke % to get the character found? Many thanks for your help, Pablo -- http://www.ousia.tk