Suggestion / wish for UNIX shell syntax highlighter

The words "case" and "esac" should be highlighted like "do" and "done". This should be easy

Only if possible:
sh/ksh/bash-like UNIX shells have a more complex syntax and it would be very helpful if more parts could be highlighted.

The full syntax for "if" is
if ...
then
...
[elif ...
then
...]
[else
...]
fi

Now, only the "if" and the "fi" are marked as belonging together. It would be nice if the "then"s and all optional parts in between were highlighted, too, because it is too easy to write
if ...
then
elif ...
...
fi
and forget the "then" after the "elif". Also, when you have nested "if"s, it would be good to see which "elif" or "else" belongs to which "if ... fi"

I know nothing about the internal highlighters, are they written by hand or do you use some publicly available module? In the latter case, I might be able to help if I knew what it is

There is a limitation for pair of the words to highlight. I can't highlight several words at once

Ok. Then the actual behaviour is the best, of course.