Where is the Header Code located?

[DeadLikeMe]

Hello,
i am new to roundcube and i am playing around a bit with the templates (styling).

I would like to change the header of a message. Can somebody tell me, where the code for this is located?
In message.html under skins/default/templates  there is only this entry:

Where do i find this "OBJECT MESSAGEHEADERS"?

Thanks in advance

[SKaero]

If you want to change it I'd recommend using the plugin api and use the template_object_* hook http://trac.roundcube.net/wiki/Plugin_Hooks#TemplateHooks