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, code completion 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 use of functions declared in user-defined modules. Such functions are not included in the code completion list and marked as unknown in the code. However, query execution in the BaseX backend works fine nonetheless.