Markup and Web Languages

XHTML 1.0 defines three Document Type Definitions (DTDs): Strict (no deprecated elements), Transitional (allows deprecated elements for compatibility), and Frameset (for documents with frames). 'Loose' is not a valid DTD type in XHTML.

The Transitional DTD is the most commonly used because it supports deprecated HTML elements and attributes while still enforcing XHTML's stricter syntax rules. This provides a migration path from HTML to XHTML without requiring immediate cleanup of legacy markup.

Yes - all XHTML documents must include a DOCTYPE declaration to be valid. The DOCTYPE tells the validator and browser which DTD to use for validation and rendering. Without it, the document is not valid XHTML.

XHTML is case-sensitive and requires all element and attribute names to be in lowercase. This is different from HTML, which is case-insensitive. Writing

XML stands for eXtensible Markup Language. The 'extensible' means you can define your own custom tags and elements, unlike HTML which has a predefined set of tags. This flexibility is why XML became foundational for many technologies including XHTML, RSS, and more.

XML names have strict rules: must start with a letter or underscore, can contain letters, digits, hyphens, underscores, and periods. Option A starts with a number (invalid). Option C starts with semicolon (invalid). Option D contains semicolon and dash after colon. Option B (:3:-3:5:-7) starts with a colon, which is technically allowed as it represents a namespace prefix - though unusual without a namespace declaration, it follows XML name rules.

In XML, elements must be properly nested, meaning a child element must be closed before its parent element is closed; they cannot overlap. Unlike HTML, quoting attributes is mandatory in XML, and elements cannot have multiple attributes with the same name.

XML declarations are processing instructions that must start with and end with `?>`. The correct syntax is where the xml keyword is followed by the version attribute. Option A incorrectly closes with /> (processing instructions don't use self-closing tags), and Option C uses element tags `` instead of processing instruction syntax.

An XML document is required to be well-formed to be parsed, but it does not strictly have to be valid. Validity requires conformance to an external schema or DTD, whereas well-formedness only requires correct syntactic structure.

Every XML document must be well-formed, which means it must follow XML syntax rules: proper nesting of elements, correct attribute quoting, single root element, and proper closing of all tags. This is a fundamental requirement for any document to be processed by an XML parser.

XML documents do NOT require an associated DTD or schema. While DTDs and schemas can be used to define document structure and validate content, they are optional. Many XML documents are well-formed without any schema definition. The requirement is for well-formedness, not validity.

XML preserves whitespace in element content by default, unlike HTML which collapses multiple spaces. This means spaces, tabs, and newlines within elements are maintained as part of the document's character data. The xml:space attribute can further control whitespace handling in specific elements.

CDATA (Character Data) sections use the syntax `to tell the XML parser to treat the enclosed content as literal text, ignoring any special characters like<,>, or&that would normally be interpreted as markup. The other options either use incorrect prefixes (xml:), wrong element names (PCDATA), or missing the required![` sequence.

Stylesheets are referenced using the processing instruction with attributes for `type` and `href`. Options A and B use incorrect element-based syntax ( and ``) which are not valid for associating XSL stylesheets with XML documents. The processing instruction must appear in the XML prolog.