Using RegEx in Apache's directives in config files and .htaccess

Question

If I understand correctly expression .ht* in the next code will match all that starts with .ht, so my .ht_lalala is safe.

<Files ".ht*">
    Require all denied
</Files>

But what about next one?

(^\.ht|~$|back|BACK|backup|BACKUP$)

Is it correct for matching files: .htaccess, back, backup, BACKUP? Or next will be better instead

(^\.ht*|back*|BACK*$)

What I'd like to understand is what ~$ actually means in my code (in RegEx pattern). I don't know why and when I put it there, but I have it in my code, and now I doubt that it's correct.

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I know basic things about RegEx, what is ^ and $, and that * means 0 or N from previous text/token, but ~ doesn't make sense inside the pattern, unless it's just a simple character and it does nothing but literally matches ~. I've read Apache docs, I guess for multiple matches FilesMatch and DirectoryMatch is better, however regular expressions can also be used on directives: Files and Directory, with the addition of the ~ character, as is stated in the docs examples.

<Files ~ "\.(gif|jpe?g|png)$">
    #...
</Files>

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And well, what I want exactly is to know how to match different files or directories.

One more thing, should I escape the .? Because default httpd.conf doesn't do so. Or it's just different for httpd.conf and .htaccess (which doesn't make sense to me)

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UPDATE

Answering to my own question, how do I match with RegEx any of this .ht, .htaccess, .htpasswd, back, BACK, backup, BACKUP, first at all I decided to use . (dot) in the name of anything I want to hide. Secondly, I found out that laconic pattern ^(\..*)$ will do the job, will give me what I need. Or ^\. even better! So, if in the future I would like to hide something, I just add the . at the start of the name.

Here we go, next code will deny access from the web to any files and directories which names start with . (tested, works)

RegEx pattern match:

<FilesMatch "^\.">
    Require all denied
</FilesMatch>

<DirectoryMatch "^\.">
    Require all denied
</DirectoryMatch>

And in brilliant explanation @MrWhite clarified and simplified my method, so I stuck with this (tested, works)

Wild-card string match:

<Files ".*">
    Require all denied
</Files>

<Directory ".*">
    Require all denied
</Directory>

Answer 1

The Apache manual covers this.

~ enables regex. Without it, you just get access to wildcards ? and *.

As far as I know Apache uses the PCRE flavor of regex.

So once you've enabled regex via ~ then use https://regex101.com/r/lPkMHK/1 to test the behavior of the regex you've written.