What is the primary purpose of using XSLT in PHP?

The primary purpose of using XSLT in PHP is to apply styles to XML documents. XSLT, which stands for Extensible Stylesheet Language Transformations, is designed specifically for the transformation of XML documents. It allows developers to define how an XML document should be rendered visually or transformed into another format, such as HTML or plain text, by using various templates and style rules.

By using XSLT, developers can separate the presentation layer from the data layer, making it easier to manage and change the display of XML data without altering the underlying XML itself. This flexibility is particularly beneficial in web applications where the same XML data might need to be presented in different ways based on user context or device.

The other options mentioned, such as converting XML into JSON format, parsing XML files, or validating XML schemas, refer to different functionalities and tasks related to XML, but do not capture the essence of what XSLT is specifically designed to achieve.