I have a related question.  I have this programming mode derived from CC mode.  The formal syntax is on the one hand much simpler than anything like C++, but I find trying to capture the constructs by the regular expression rules employed by font lock very difficult to get right.

I have a re-entrant LALR grammar for this language that I intend to use with Semantic to get proper handling of all constructs.  That's one of the main reasons I wanted to be sure to get as efficient a baseline system as possible (and can now proceed with).

I'm curious, though, as to why Semantic/CEDET seems to have been superceded by external solutions like tree-sitter or LSP-based (non-emacs) servers.  One of the draws of Emacs for me is the "batteries included" nature of it having Emacs Lisp built in.  Is there a downside to using Semantic as the basis for improving my derived mode that's non-obvious?  Would producing a threaded code parser instead of a straight table driven parser be a better approach with the native compilation option now available?

I also use this mode to fontify a REPL session for this language, which has pretty awful performance when producing tracing output that hits 1-5 hundred K lines in a buffer, which is why this narrowing discussion interests me, even though the buffers in question don't have particularly long lines.  It just chews up memory if I try to jump from the end of the buffer to the beginning. Or at least it did in v24.3.

Thanks,

Lynn