distinguish inner consecutive spaces

Question

I'm aware of and use whitespace-mode to great effect. I don't show a glyph/character for spaces because I think it's too noisy and unnecessary. I do highlight trailing spaces red which is great.

Aside from that, I was thinking that it may be useful to specify a glyph such as ·, if it were possible, for inner consecutive spaces. This means that it excludes trailing whitespace as well as indentation, for example:

print("one·····two");

instead of:

print("one     two");

But again, this wouldn't apply to leading/indentation whitespace nor trailing whitespace.

Is this possible?

EDIT: I tried setting whitespace-regexp-search as:

(setq whitespace-space-regexp "[^ ]\\( \\{2,\\}\\)[^ ]")

I have spaces and space-mark in my whitespace-style:

(setq whitespace-style
      '(face indentation trailing empty spaces space-after-tab
        space-before-tab tab-mark space-mark))

However, it seems like the whitespace-space-regexp is only for the spaces face highlighting, and isn't used for setting the space-mark. Here's the effect:

Notice that all other spaces are still showing the space-mark, even though what I'd like is for consecutive spaces of 2 or more to show it. The inner consecutive spaces are indeed being highlighted differently, but I only did that to show the difference between what's being matched by whitespace-space-regexp and the space-mark character.

In fact I just noticed that even the numberline is showing the space-mark.

It looks like the space-mark is simply matched based on a character, which I guess makes sense, so perhaps this isn't possible after all.

Note: As outlined in my post, I recognize that this isn't possible via whitespace itself, what I'm curious about is whether it's possible to do at all. I found some uses of font-locking such as this one which accomplish replacing pattern matches with a character. I'm wondering if it would be possible to use something like this but have it replace the spaces in the region matched with the middle dot for example.

Answer 1

Indeed you can't specify different glyphs for different kinds of spaces because this feature makes use of a display table. The relevant values in variable whitespace-style are (emacs manual):

space-mark Draw space and non-breaking characters with a special glyph.

tab-mark Draw tab characters with a special glyph.

newline-mark Draw newline characters with a special glyph.

All other values specify highlights, so all other distinctions can only be made through the use of faces.

See my answer on a related question.