Question: For the given text:

> 
> This text A,is separated,by a comma A,unpreceded by the uppercase A,letter A,ok?,
> 
> 
> 

Expected matches:

> 
> This text A,is separated,
> 
> 
> 

and

> 
> by a comma A,unpreceded by the uppercase A,letter A,ok?,
> 
> 
> 

Please write a regex that would work like described. Preferably one that will work with .NET

Answer: 
I think the regex feature you're after is negative lookbehind. Try splitting on this regex:

```
(?<!A),

```

Eg. 

```
new Regex(@"(?<!A),").Split("This text A,is separated,by a comma A,unpreceded by the uppercase A,letter A,ok?,");

```
```
static void Main(string[] args)
{
    string s = "ThisA,textA,isA,separated,byA,theA,absenceA,ofA,theA,letterA,\"a\",";
    string pattern = "[^A],";
    int startIndex = 0;
    foreach (Match line in Regex.Matches(s, pattern))
    {
        string chunk = s.Substring(startIndex, (line.Index + 1)-startIndex);
        Console.WriteLine(chunk);
        startIndex = line.Index + 2;
    }
    Console.Read();
}

```