I believe they mean the operators and operands are all mixed up, eg in `ab`, and this makes it so you have to escape all sorts of characters, but if you split it into `"a" "b"` then the separation is clear
I mean it isn't clear whether a character is a control character (* + ? [ ] - etc) or a literal character because they're all mixed up. The rules about which is which are too complex, extensive and varying.
If you use syntax like "a"* "b" then it's really obvious - the stuff in quotes is literal text, everything else is control.
Could you explain this? I don't quite understand what the problem is. Do you mean something like sed's regex substitute command?