advanced Gtk+ HTML editor
Bluefish is a GTK+ HTML editor for the experienced web designer. Its features include nice wizards for startup, tables and frames; a fully featured image insert dialog; thumbnail creation and automatically linking of the thumbnail with the original image; and configurable HTML syntax highlighting.
For validation to work you need weblint and xmllint. For preview to work, you need a web browser that can view local files given to it on the command line.