It means the XML adheres to the syntax rules, like having a single root element, properly nested tags, and quoted attributes.

No, this tool only checks for syntax errors (well-formedness), not schema compliance.

Yes, the validation is performed entirely within your browser using the DOMParser API.

XML is widely used for configuration files, data exchange between systems, web services (SOAP), RSS feeds, SVG graphics, office document formats (DOCX, XLSX), and as a general-purpose data serialization format.

Well-formed XML follows the basic syntax rules and can be parsed successfully. Valid XML not only is well-formed but also conforms to a specific schema (XSD or DTD) that defines the allowed structure and data types.

Common causes include unclosed tags, missing the XML declaration, special characters that aren't properly escaped (like &, <, >), attributes without quotes, or multiple root elements. Check the error message for the specific line number.

The XML declaration (<?xml version='1.0'?>) is recommended but not mandatory for well-formedness. However, it's best practice to include it, especially when specifying character encoding.

Special characters must be escaped: & becomes &amp;, < becomes &lt;, > becomes &gt;, " becomes &quot;, and ' becomes &apos;. Alternatively, you can use CDATA sections for blocks of text containing special characters.

Yes, as long as they are well-formed XML documents. XHTML and SVG are XML-based formats, so this tool can check their syntax. However, it won't validate against XHTML or SVG-specific schemas.

XML is stricter and more rigid: all tags must be closed, attribute values must be quoted, and it's case-sensitive. HTML (especially HTML5) is more forgiving and allows unclosed tags and unquoted attributes in many cases.