Huh? What are you talking about?

Since this is, to my memory, the first time anyone has suggested what you are suggesting is possible, I assumed that you had to be talking about the new 5.14 regex modifiers: a, d, l and u These modifiers, new in 5.14, affect which character-set semantics (Unicode, ASCII, etc.) are used, as described below in Character set modifiers."

Of course, if you would demonstrate rather than allude, it wouldn't be necessary for all us lesser beings to guess what you are alluding to with your pronouncements from on high.

Match 400 any true characters (not code points):

$some_modern_text_in_a_plural_world =~ m/\X{400}/;
[download]

See Character Classes and other Special Escapes in perlre and Misc in perlrebackslash.

\X [4] Match Unicode "eXtended grapheme cluster"

Hm. So let me see if I have this right.

1. Because the OP mentioned the word "characters" -- even though he didn't mention unicode (Oops. PST) Unicode -- you are saying that we can no longer use the regex metachar '.', because we don't know that it won't be Unicode, and we therefore run the risk of splitting an "eXtended grapheme cluster".
2. Which in turn implies that we should never use the '.' metachar.
3. Which of course begs(PST) leads to the questions:

   Why have '.' if you must always use \X instead?

   Why not simply replace the '.' semantics with the \X semantics and have done with it.

I suspect the reason is PST, but I'll keep an open mind.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.