Symphony.

Which version of IE are you using? I don't expect anyone has ever tested the debug mode with IE...

IE 8 ...

Doing development on my precious iMac with Safari so no worries ... Just using other machines to test the outcome ...

I don't think it'd be a bad idea to look at the Devkit markup. There is probably a much cleaner way to do it then the current implementation. The following is the markup generated for one line.

<line id="4" class="selected">
    <marker></marker>
    <content>
        <span class="context-markup xml">
            <span class="text" index="3"></span>
            <span class="tag open" index="4" handle="3x2">
                <span class="begin">&lt;today</span>
                <span class="end">&gt;</span>
            </span>
            <span class="text" index="5">2011-04-28</span>
            <span class="tag close" handle="4x3">&lt;/today&gt;</span>
            <span class="text" index="6"></span>
        </span>
    </content>
</line>

Beyond removing content I don't know if it can be much cleaner, given the flexibility of syntax highlighting this affords.

I've tried to install Symphony without any extension but seems that the debug devkit is required by installer ...

That sounds weird ...