If an XML document does not include a DTD (Document Type Definition), what is it considered with respect to type validity?

Introduction / Context:
Validation in XML checks whether a document conforms to a declared grammar such as a DTD or XML Schema. The terms “type-valid” and “not-type-valid” hinge on the presence of, and conformance to, that grammar.

Given Data / Assumptions:

• No DTD is provided in or for the document.
• We are using traditional terminology where DTD-based validation defines type validity.
• Well-formedness (proper syntax) is separate from validity (conformance to a grammar).

Concept / Approach:
If a document lacks a DTD (or other schema) to validate against, it cannot be declared type-valid. It may still be well-formed, meaning it satisfies XML’s syntax rules (proper nesting, single root, quoted attributes). But “type-valid” requires a declared grammar and successful validation.

Step-by-Step Solution:

Verification / Alternative check:
XML tools distinguish “validate” actions (requiring a DTD/XSD) from “well-formed” checks. Without a DTD/XSD, validation reports “no grammar” rather than “valid.”

Why Other Options Are Wrong:
type-valid: Requires a grammar and successful validation.
an HTML document: XML without DTD does not become HTML.
None: Incorrect because the defined term is “not-type-valid.”

Common Pitfalls:
Confusing “valid” with “well-formed.” Many XML pipelines accept well-formed documents even without validation.

Final Answer:
not-type-valid.