XPath and XSLT support
XSLT support is available in all XML files that declare the XSLT-Namespace http://www.w3.org/1999/XSL/Transform on their root element.
PhpStorm lets you evaluate expressions against the currently focused document, including support for the document() function to make cross-document queries. You can also evaluate an expression against multiple XML documents in the Find in Files style using the Find by XPath action.
You can configure to highlight matching expressions in the current editor or to show a list of matching lines in the Find tool window. Editing XPath expressions is enhanced by on-the-fly error-checking including a set of customizable XPath inspections and a wide range of code completion suggestions.
PhpStorm also lets you display a unique XPath expression for a selected element in the editor by choosing from main menu.
XSLT support is not limited to XPath expressions, it also supports a wide range of XSLT constructs, like checking the existence of templates that are called via xsl:call-template and their parameters, refactoring and navigation enhancements.