[Dev-luatex] \prehyphenchar

Hello, LuaTeX snapshot-0.20.2-2007121721: This works (in PlainTeX): \prehyphenchar`\- This results in an error: \prehyphenchar=`\- ! Missing number, treated as zero. <to be read again> = l.29 \prehyphenchar= `\- A bug? Am I misunderstanding something? Jonathan