Bluefish is a powerful editor for experienced web designers and
programmers. Bluefish supports many programming and markup languages,
but it focuses on editing dynamic and interactive websites. See
features for an extensive overview, take a look at the screenshots,
or download it right away. Bluefish is an open source development
project released under the GPL license.

If you want to build Bluefish with GTK2,

GTK2=yes ./bluefish.SlackBuild

otherwise GTK3 will be used by default.

js-beautify is an optional run-time dependency used if installed
(not available on Slackbuilds.org). 

NOTE: 
This is the last version compatible with 15.0.
Never versions will require glib >= 2.76
