Regular Expression for AppSettings Tags Removing commented tags

I would like to create a regular expression which should give me the only those appsettings tags which are not commented. Following is the test string.

<a key="a" value="b"/><b key="b" value="b"/><!--<c key="c" value="c"/>-->
<d key="d" value="d"/>

I've come up with following regular expression so far.

(?<!<!--)<[^>]*/+>

Her i'm testing the negative lookahead of

<!--

but it's not working. Any idea.

Solution

This is another good opportunity to apply the trash can approach: everything we want goes into the 1st capturing group, the rest goes into the overall match and will be completely disregarded.

A regex that achieves just that could look like this:

<!--.*?-->|(<\s*\w+[^>]*>)

Explanation:

 the first alternation matches HTML comment blocks and everything between lazy
(<\s*\w+[^>]*>) the second matches any simple XHTML tag

Demo

So, only if there is a value in $1 we take note of it.

Sample Code:

using System;
using System.Text.RegularExpressions;

public class Example
{
    public static void Main()
    {
        string pattern = @"<!--.*?-->|(<\s*\w+[^>]*>)";
        string input = @"<a key=""a"" value=""b""/><b key=""b"" value=""b""/><!--<c key=""c"" value=""c""/>-->
<d key=""d"" value=""d""/>";
        RegexOptions options = RegexOptions.Multiline;

        foreach (Match m in Regex.Matches(input, pattern, options))
        {
            if(m.Groups[1].Success)
                Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
        }
    }
}

Another pattern that could achieve a similar thing is to make use of negative lookarounds to assert the comment tags:

(?<!<!--)(<\s*\w+[^>]*>)(?!-->)

Demo 2