I expect the most noticeable change from this PR is that string contents and the quotes around strings are now separate lexical classes with potentially different appearance.

This PR undoes 94cf367 for After which is an unused struct.

There are other data type (lineState), function (getLexicalClass), and variable(lexicalClasses) definitions in this that are globally visible which can cause name clashes and multiple definition errors. For functions and variables, static can be used to prevent visibility to other modules but that doesn't work for class definitions. An unnamed namespace can be wrapped around all the definitions in the file except for lmVisualProlog to hide them from other modules. There is no need for static inside the unnamed namespace.

using namespace Lexilla;

namespace {
...
}

LexerModule lmVisualProlog(SCLEX_VISUALPROLOG, LexerVisualProlog::LexerFactoryVisualProlog, "visualprolog", visualPrologWordLists);

g++ and clang++ dislike getState:

clang++ -D_CRT_SECURE_NO_DEPRECATE=1 -DNDEBUG -I ../include -I ../../scintilla/include -I ../src -I ../lexlib --std=c++17 -O3 -Wpedantic -Wall -Wextra   -c ../lexers/LexVisualProlog.cxx -o LexVisualProlog.o
../lexers/LexVisualProlog.cxx:320:64: warning: '&' within '|' [-Wbitwise-op-parentheses]
        return verbatim << 31 | closingQuote << 16 | kindStack & 0xFFFF;
                                                   ~ ~~~~~~~~~~^~~~~~~~
../lexers/LexVisualProlog.cxx:320:64: note: place parentheses around the '&' expression to silence this warning
        return verbatim << 31 | closingQuote << 16 | kindStack & 0xFFFF;
                                                               ^
                                                     (                 )
1 warning generated.

Yes, that is the most "visible" change (I forgot to mention it).
I have mapped old and new states to give the best possible styling in e.g. Notepad++ (though I don't think they have moved to this version yet).

String and verbatim strings have same style now (what used to be the verbatim style) and the quotes have the old string style.

I have updated the code according to your comments.

(Putting it inside an anonymous namespace made Visual Studio reformat a number of things).

Putting it inside an anonymous namespace made Visual Studio reformat a number of things

Visual Studio puts these in a separate undo transaction and if you press Undo immediately after, just the formatting reverts. The changes show you have Visual Studio formatting options (Options | Text Editor | C/C++ | Code Style | Formatting) different from how you have previously formatted this code. I'll probably split out an initial formatting commit so the main commit is mostly behavioural changes.

I assume/guess that will mean creating another PR. And then rebasing this one on top of that?

I assume/guess that will mean creating another PR. And then rebasing this one on top of that?

I've not had much success with fixing things up inside the GitHub PR process. I have a copy of your end state and I'll use WinMerge to compare to a reformat (either with Visual Studio or astyle), commit that; then move other differences into a second commit. I want to make it easy to see the real differences and ignore the formatting differences.

Is there documentation that can be linked for embedded and placeholder? I couldn't find anything in the VisualProlog Language Reference.

No, (currently) embedded syntax + placeholders is an undocumented feature.

Unfortunately, it turned-out that placeholders always need "manual" qualification to resolve ambiguities, and that is quite cumbersome to deal with. So even though we use it ourselves, I am not sure if other people will start using it (which is of course self-fulfilling until I write some documentation (but even then)).