A rewrite from scratch of the venerable TeX typesetting software, in Lua, with better support for frames and grid, native i18n and XML support.
I don’t see what’s the difference to luatex. Is there any, apart from SILE not being compatible? Is there any advantage?
It looks like SILE is more of a from-scratch implementation. It doesn’t contain any of the original Knuth TeX code in it, though it does borrow some of his algorithms (like the line-breaking algorithm). Luatex, by contrast, is pdftex extended with an embedded Lua engine, and pdftex is the original Knuth TeX extended with PDF output (among other things). The main advantage to not being TeX-heritage is much cleaner code that you’re not as afraid to touch, I would guess; the original TeX is very hairy ‘70s code written in WEB auto-translated to C.
Besides that, the main high-level difference I can see is that SILE is built around an InDesign-style model where text flows between frames.
luatex is AFAIR not written in WEB anymore. It’s a nearly complete rewrite to support bidirectional and grid typesetting, and afaict it also deals pretty well with flows between frames. At least context mark IV could do that pretty impressively. I’d appreciate an answer from someone who worked/looked deeply on luatex and SILE, because I find it hard to form an opinion.
I’m not really familiar with luatex internals, but I did briefly browse its repository before posting and saw web2c still in there, which I took as a sign that vestiges of the old WEB code are still in there somewhere. Or is it just in the repo because nobody’s removed it?
The author also mentioned that he wanted to tackle some things that TeX cannot do, like match up the lines with those from the previous page. I believe that he works/worked with bible printing and the thin paper demands alignment between the paper sheets.
That’s something that luatex can do (since before 2010, when I set did that first).
Huh alright, I didn’t know that. Thanks for mentioning it.