XML (eXtensible Markup Language) is a markup language that defines rules for encoding documents in a format that is both human-readable and machine-readable. It uses tags to structure data.

What is the difference between well-formed and valid XML?

Well-formed XML follows basic syntax rules (closing tags, proper nesting, quotes around attributes). Valid XML additionally conforms to a DTD or XSD schema that defines the allowed structure.

DTD (Document Type Definition) defines the legal building blocks of an XML document, including element types, attributes, and their relationships. It can be internal or external to the document.

XSD (XML Schema Definition) is a more powerful alternative to DTD for defining XML structure. It supports data types, namespaces, and constraints, and is itself written in XML.

/ /XML Formatter / Validator

XML Formatter / Validator

Format, validate, and minify XML. Check that your XML is well-formed, apply consistent indentation, or compress it by removing unnecessary whitespace.

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Frequently Asked Questions

What is XML?: XML (eXtensible Markup Language) is a markup language that defines rules for encoding documents in a format that is both human-readable and machine-readable. It uses tags to structure data.
What is the difference between well-formed and valid XML?: Well-formed XML follows basic syntax rules (closing tags, proper nesting, quotes around attributes). Valid XML additionally conforms to a DTD or XSD schema that defines the allowed structure.
What is a DTD?: DTD (Document Type Definition) defines the legal building blocks of an XML document, including element types, attributes, and their relationships. It can be internal or external to the document.
What is XSD?: XSD (XML Schema Definition) is a more powerful alternative to DTD for defining XML structure. It supports data types, namespaces, and constraints, and is itself written in XML.
What are XML namespaces?: Namespaces prevent element name conflicts by prefixing tags with a unique identifier (URI). For example, <ns:element xmlns:ns="http://example.com"> associates element with the namespace.
What is CDATA?: CDATA (Character Data) sections allow including raw text that should not be parsed as XML. Written as <![CDATA[ ... ]]>, it is useful for embedding code or special characters.
How does XML compare to JSON?: XML is more verbose but supports attributes, namespaces, and schemas. JSON is lighter, native to JavaScript, and preferred for web APIs. XML remains strong in enterprise and document-centric applications.
What is XPath?: XPath is a query language for selecting nodes from XML documents. It uses path expressions like /root/child/element to navigate the tree structure of XML.
What is XSLT?: XSLT (eXtensible Stylesheet Language Transformations) is a language for transforming XML documents into other formats like HTML, text, or other XML structures using template rules.
What is SOAP?: SOAP (Simple Object Access Protocol) is an XML-based messaging protocol for exchanging structured information in web services. It uses XML envelopes with header and body sections.
How do I handle special characters in XML?: Use XML entities: &lt; for <, &gt; for >, &amp; for &, &apos; for ', &quot; for ". Alternatively, wrap content in CDATA sections.
What is the XML declaration?: The XML declaration is an optional line at the top: <?xml version="1.0" encoding="UTF-8"?>. It specifies the XML version, character encoding, and standalone status.
Can XML have empty elements?: Yes, empty elements use self-closing syntax like <br /> or <element></element>. Both forms are valid and equivalent in XML.
What is XSD and how is it different from DTD?: XSD uses XML syntax, supports data types (string, integer, date), and allows defining min/max occurrences. DTD uses non-XML syntax and has limited type support. XSD is more widely used today.