gtksourceview
GtkSourceView is a portable C library that extends the standard GTK+ framework for multiline text editing with support for configurable syntax highlighting, unlimited undo/redo, UTF-8 compliant caseless searching, printing and other features typical of a source code editor.
SlackBuild
http://slackbuilds.org/repository/14.0/libraries/gtksourceview/
Package 32 bit: gtksourceview-2.11.2-i486-2_SBo.tgz