The plugin is very well maintained! It adds support for various XQuery Implementations to the IntelliJ IDEA (among them BaseX). It provides syntax highlighting for XQuery and XML and detects syntactical errors while you type offering a description for each error. Queries are executed using Run Configurations for which you can configure various query processors, e.g. BaseX.
The plugin contains some minor flaws regarding the static binding of BaseX namespaces. Also, the IntelliJ ''Find Usages'' and ''Go To'' options did not work as expected in some cases, especially with regard to functions and across modules. The plugin does not yet include a code completion feature.