The definitions in an XML document are said to be __________ when the tagging…

Correct answer: valid.

Explanation: An XML document is well-formed if it follows XML syntax rules (properly nested tags, a single root element, matching start/end tags, and quoted attribute values). It is valid when it is well-formed and also conforms to the element and attribute declarations in an associated DTD or XML Schema.

• Well-formed: ensures correct XML syntax but says nothing about whether element names, allowed children, or attributes match a DTD/schema.

• Valid: additionally requires that the document's structure and tag usage conform to rules defined in the DTD or Schema (element declarations, allowed content, attribute lists, etc.).

• How this matches the question: the phrase "tagging system and definitions in the DTD are all in compliance" describes conformity to the DTD, which is the definition of a valid XML document.

• How to check: use an XML parser with validation enabled or an online validator to verify that the document conforms to its DTD or Schema.