Documenting XSLT
IntelliJ IDEA comes with bundled documentation for XSLT elements and functions that is accessible via the Quick Documentation Lookup Ctrl+Q action. This documentation is extracted from the respective sections in the official W3C XSLT and XPath documents.
It's also possible to annotate elements in an XSLT Style Sheet with documentation fragments. This can be looked up by the Quick Documentation Lookup function for variables, parameters, and templates
Enable the XPathView + XSLT plugin
This functionality relies on the XPathView + XSLT plugin, which is bundled and enabled in IntelliJ IDEA by default. If the relevant features aren't available, make sure that you didn't disable the plugin.
Press Ctrl+Alt+S to open the IDE settings and then select .
Open the Installed tab, find the XPathView + XSLT plugin, and select the checkbox next to the plugin name.