Markup and Web Languages

DTD stands for Document Type Declaration. It defines the structure and legal elements of an XML or XHTML document, telling parsers which tags and attributes are valid.

XHTML is defined as a subset of SGML (Standard Generalized Markup Language), just as HTML is. SGML is the parent meta-language from which both HTML and XHTML derive their rules. Option A is incorrect because HTML and XHTML are subsets of SGML, not the reverse.

The statement in option A is false - XHTML documents ARE parsed by browsers before display. Options B, C, and D are all true statements: XHTML uses DTDs, the doctype declaration specifies which DTD to use, and XHTML requires well-formed syntax. Since the question asks which statement is false and A is marked as correct (meaning A is the false statement), this is consistent.

XHTML is often considered more 'advanced' or 'rigorous' than HTML because it applies XML's strict syntax rules to HTML. This makes it easier for automated tools to parse and process, though HTML5 has since bridged many of these gaps.

Option A makes the least sense because XHTML was specifically designed to address HTML's problems and was expected to replace it for professional development. Options B, C, and D all reflect the historical reality: XHTML was intended as an HTML replacement, HTML had known issues, and XHTML was being adopted. The framing suggests A is the answer because it contradicts the XHTML migration trend of the early 2000s.

XHTML should be validated to ensure it conforms to its DTD and is properly well-formed. Validation catches syntax errors and ensures compatibility across browsers. Option C correctly states that validation is beneficial.

For XHTML to function properly, documents must be both valid (conform to DTD) and well-formed (properly nested, closed tags, quoted attributes). XHTML syntax is case-sensitive and requires lowercase elements. Option B is correct.

In XHTML, all element and attribute names must be in lowercase. While the content between tags can contain uppercase letters, the tags themselves must be lowercase. Additionally, all tags must be closed (e.g., ), and the document must be well-formed.

In XHTML, all attribute values MUST be enclosed in quotes (single or double). This is a strict requirement differing from HTML where quotes were sometimes optional for simple values. Option B is correct.

XHTML is a stricter, XML-based version of HTML. One of its primary rules is that all tags must be in lowercase. Therefore,

XHTML requires all elements to be properly closed. For empty elements like line breaks, this means using the self-closing syntax with a space before the slash:
. Option D is correct. The traditional HTML
is invalid in XHTML.

XHTML requires all attribute names and values to be in lowercase, and attribute values must be quoted. The correct format is width="80" (all lowercase, quotes around value). Option B is correct. Options A and D use uppercase, and option C lacks quotes.

XHTML is stricter than HTML - every element must be properly closed, including empty elements which use self-closing syntax like
or . This is a fundamental rule that distinguishes XHTML from HTML.

The DOCTYPE declaration is not an HTML/XHTML element - it's a document type declaration that tells the browser which version of HTML/XHTML to use. Declarations, unlike elements, do not have closing tags.

XHTML documents require a complete structure: the DOCTYPE declaration at the top, then as the root element, which must contain and sections. The section must contain a element.