This is a time-based release, scheduled to come out about 1 year after jEdit 5.4, and is a collection of enhancements, bug fixes and patches submitted by the community. Detailed changes can be found in the Detailed Change Log.
One notable new thing in this version is autosaves of untitled buffers. This allows jEdit to save and restore untitled buffers across sessions. Totally rewritten is most of the autosave code - it can use an autosave directory to store its files. In addition, the option for never marking untitled buffers dirty has been replaced by an option that achieves a similar goal (allowing you to close or quit untitled buffers without a dialog confirmation), but allows for multiple dirty untitled buffers.
jEdit's launcher and core have both been tested with Java 9. Some of the plugins (e.g. Lucene) may not yet be compatible, but at least the core works fine on it now.
With continued support from the community, we will keep releasing a newer version each year that can accurately bring together the fruits of everyone's labor. Thank you to each and every one of the contributors who helped make 5.5 the best version of jEdit ever.