[Vb.net] how to split string with multiple delimeter but keep delimeter

In a Regex, dot '.' has a specific meaning: "any character". So a regex of "a.b" will match "aab", "abb", "acb", ... any character between an a and a b.
So your regex: "(.|,)" is "either any character or a comma" - which amounts to "any character!

You can escape it so that it becomes a literal: "(\.|,)" which is "either dot or comma" but for single character values there is a better syntax: "[\.,]" which does the same thing.

Quote:

A regex for string.split(regexp) would be preferable

Advice: study RegEx, there is more than 1 way to use it.
Split is used to cut a string on separator and separator is lost.
Match on the other side will make a list of every match in string. you just have to build a RegEx that will match "a word or a point".
A RegEx like \w+|\. should all what you want.

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx: Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
This site also show the Regex in a nice graph but can't test what match the RegEx: Regexper[^]

Try this:

Dim s As String = "Yellow.car Red.Bag Blue.eyes"
s = s.Replace(".", " . ")
Dim result = String.Join(",", s.Split(New String(){" "}, StringSplitOptions.RemoveEmptyEntries).Select(Function(w) String.Concat("'", w, "'")))

Result:

'Yellow','.','car','Red','.','Bag','Blue','.','eyes'

As you see, the logic is very simple:
1) replace dot with dot with spaces around it,
2) split string on spaces and add ['] around each part,
3) join parts with commas.

That's all!