If you process the following with (plain) pdftex %&pdflatex
\stop then you get This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015) (preloaded format=pdflatex) showing that the first line comment has been read to load pdflatex.fmt The analogous file for (plain) luatex %&lualatex \stop produces This is LuaTeX, Version beta-0.80.0 (TeX Live 2015) (rev 5238) restricted \write18 enabled. (./xx.tex ! Undefined control sequence. l.3 \stop showing that the file is being processed by plain. luatex --help and page 30 of the (0.80) manual indicate that there are --(no-)parse-first-line command line options which at least implies that the web2c style first line parsing should be active? If it isn't intended to work could those options be removed thanks, also in that case is it possible to do a similar thing from lua at the top of the file? The use case where I found this was a bunch of test files using different formats and wanted to simply loop over them with information within the file as to which format to use, rather than maintaining the information about which format to use for each test separately. David
