I did following:
1) In Windows 7: Under registry: HKEY_CLASSES_ROOT\PROTOCOLS\Handler
I have my custom protocol calls: stackoverflow (copied similar way in registry like other protocols mailto or ftp etc)
2) Open in IE the sample: http://jsfiddle.net/L528u/
<a href="stackoverflow:talking" id="link1">CLICK IT</a>
<button onclick="alert(document.getElementById('link1').protocolLong);">CHECK - IF - Protocol available or not</button>
3) when click the button from IE to detect the protocol: stackoverflow it fails
I get always alert box: "Unknown protocol" but when i try to detect protocols like: ftp, mailto it works
<a href="ftp:talking" id="link1">CLICK IT</a>
<button onclick="alert(document.getElementById('link1').protocolLong);">CHECK - IF - Protocol available or not</button>
Question: Can anyone please tell me what is missing in registry entry for to activate the new protocol? "stackoverflow" (where ftp, mailto works but not stackoverflow)