In C++ syntax, the following line doesn’t enter string highlighting mode at the start of the string, but at the end. The rest of the file is highlighted as a string, except for strings which are highlighted as code:

a() + "#"

It only happens when this pattern occurs at global scope, not in a function. It can happen naturally in a constructor initializer (or macro definition, etc):

Foo::Foo () : foo(bar() + "#") { ... } #define foo bar() + "#"
The # can be replaced with other things for different effects. E.g. “/*” will start a block comment.

Sublime 3 3033 (Linux)