SEO: XSL article, SoftwareApplication schema, improve testing article

site/layouts/partials/schema-app.html

@@ -0,0 +1,26 @@
+<script type="application/ld+json">
+{
+  "@context": "https://schema.org",
+  "@type": "SoftwareApplication",
+  "name": "XSLT Playground",
+  "url": "https://xsltplayground.com",
+  "description": "Free online XSLT editor, tester and validator. Run XSLT 1.0, 2.0 and 3.0 transformations in your browser using Saxon. No install required.",
+  "applicationCategory": "DeveloperApplication",
+  "operatingSystem": "Any",
+  "offers": {
+    "@type": "Offer",
+    "price": "0",
+    "priceCurrency": "USD"
+  },
+  "featureList": [
+    "XSLT 1.0, 2.0 and 3.0 support",
+    "Saxon-powered backend",
+    "Real-time XML transformation",
+    "XSLT validator with detailed error messages",
+    "Multiple workspaces",
+    "Execution trace and debugging",
+    "Multiple XML inputs and parameters",
+    "Import/Export workspaces as JSON"
+  ]
+}
+</script>