In the context of GSoC, we worked hard to get a new search finished. We need to update all documentation, create a blog post, etc.
TL;DR: We updated the search to Apache Lucene. The syntax is explained at Searching externally using Online Services | JabRef. Try it out - but ensure that you made a backup of your library.
The pull request switching to Apache Lucene is close to a merge. We now aim for feedback. Both for show stoppers and improvements, we should target for 6.0 release of JabRef. We noticed that JabRef’s v5.x Simple Search sometimes did not work. Thus, we did not convert these kinds of searches.
The current implementation does not support a) case sensitive search and b) exact matches. “exact matches” mean that a search for “apple” DOES NOT match “pineapple”. It can be achieved by using regular expression search for [^\w]apple[^\w] IMHO.
Call for action: Download the Lucene search build and try if it works “OK” enough to be included in a developer build.