This is a list of documents to start with:
Currently, a document Problems with FLTK is maintained, ideally, it will be removed soon.
There are several classes etc., which are used for tasks formerly (in the GTK+ version of dillo) achieved by GtkObject (in 1.2.x, this is part of Gtk+) and GLib. For an overview on all this, take a look at Lots of Useful Tools.
GtkObject is replaced by the following:
As an alternative to the macros defined in list.h, there is also a template class, lout::misc::SimpleVector, which does the same.
If you have been familiar with Dw before, take a look at Changes to the GTK+-based Release Version.