'gentle' lets you be gentle to your markup.
If you have worked with ERb or HAML, which you very likely have, since you are looking into gentle, you might have found yourself cutting and ripping HTML templates into pieces spreading their locigal sections over multiple files. gentle considers this being a tedious task and seeks to simplify it - if not making it joyful.
For 'gentle' html templates and html mockups are the same. gentle loads a mockup and transforms it. views are described as pairs of selectors and transformations.
gentle is mainly inspired Christophe Grand's Enlive (implemented in Clojure). And it has to be said: Not only Enlive but also Clojure are awesome.
gentle can be used with Ruby On Rails as a templating engine much like Hampton Caitlin's HAML. In filename endings 'gentle' is shortend by leaving out the vowels (e.g. some_view.html.gntl).
'gentle's transformators are based on Nokogiri. Aktually gentle has a builtin fallback to Nokogiri::XML::Node. So, for those familiar with Nokogiri, there isn't much to learn here.
gentle doesn't come up with it's own terminologies for transformations. Since it is so greatly influenced by Enlive it sticks to Enlive's naming scheme[1]. For ease of use it provides some aliases following jQuerys naming scheme[2], and finally since it's built on top of Nokogiri provides Nokogiri::XML::Node's naming scheme[3], as a fallback.