As a web developer in today’s digital landscape having strong XHTML skills is crucial for building fast, accessible, and standards-compliant websites. XHTML combines the familiarity of HTML with the strict syntax rules of XML making it a powerful tool for developing semantic, SEO-friendly markup.
With XHTML being a commonly tested skill in web developer interviews, it’s important to be well-prepared to showcase your proficiency. This article provides 20 of the most frequently asked XHTML interview questions, along with detailed explanations and sample code to help reinforce your learning.
1. What are the key differences between HTML and XHTML?
XHTML is a stricter, cleaner version of HTML that follows XML syntax rules. The key differences include:
Case sensitivity – XHTML tags must be lowercase
Closing tags – All elements must have closing tags
Quoted attributes – Attribute values must be enclosed in quotes
Proper nesting – Tags must be properly nested
Self-closing tags – Elements like <img> must use trailing slash
Root element – Documents must have single top level element
HTML is more forgiving and allows practices like omitting quotes or closing tags.
2. How can you ensure an XHTML document is well-formed?
To ensure well-formedness in XHTML:
All tags must be properly nested and closed
Lowercase tag names must be used consistently
Attribute values should be quoted
Self-closing tags like <br /> should be used for empty elements
The document must adhere to its DOCTYPE declaration
Avoid using deprecated elements like <font>
Well-formedness is key for consistent rendering across browsers.
3. What is the significance of the DOCTYPE declaration?
The DOCTYPE declaration specifies the HTML/XHTML standard used by the document. It ensures:
Browsers render using standards mode for consistency
Markup is validated for well-formedness
Document adheres to W3C web standards
Enables use of newer HTML5/XHTML features
Without it, browsers may use quirks mode leading to unexpected rendering.
4. When is XHTML preferred over HTML?
The stricter syntax of XHTML makes it preferable when:
Strong validation is required, like XML web services
Compatibility with other XML-based languages is needed
Support for XML tools like XSLT/XPath is desired
Clean, well-structured markup is critical
Forward compatibility with HTML5 is important
However, HTML5 provides similar benefits without XHTML’s syntax rigor.
5. What tools can you use to validate XHTML documents?
Some commonly used XHTML validation tools:
W3C Markup Validation Service – Validates documents by direct input, file upload or URI
Browser Developers Tools – Highlight errors and warnings directly in the browser
HTML Tidy – Identifies and fixes markup errors
Online services like XHTML Validator
Build tools like Grunt, Gulp, Webpack using plugins for automated testing
6. How are namespaces handled in XHTML?
Namespaces prevent naming conflicts when mixing XHTML with other XML vocabularies. The xmlns attribute declares the default namespace:
xml
<htmlxmlns="http://www.w3.org/1999/xhtml">
Additional namespaces can be declared to embed other languages like MathML:
CDATA sections prevent parsing errors from special characters.
9. Why must XHTML be served as XML rather than HTML?
As XHTML is XML-based, serving it as text/html can cause errors in XML-aware user agents. Using the proper XML MIME type like application/xhtml+xml ensures:
Browsers parse it correctly as XML
Well-formedness rules are enforced
No risk of corruption from misparsing
This respects a core XML principle – robustness through strict well-formedness.
10. How does error handling differ between HTML and XHTML?
XHTML handles errors strictly by stopping parsing altogether when well-formedness rules are violated.
HTML uses error recovery to try and continue parsing erroneous markup. This leads to inconsistencies across browsers and makes debugging harder.
For XHTML, validation should be done before deployment. IDEs with error detection help avoid mistakes.
11. What is element minimization and why is it prohibited in XHTML?
Element minimization refers to omitting certain parts of a tag, like closing tags or attribute values.
This is allowed in HTML but prohibited in XHTML because:
XML requires all elements to be properly closed
Omitted values create ambiguity in document structure
Well-formedness depends on complete markup
This strictness results in reliable parsing across different XML processors.
12. Why is case sensitivity important in XHTML?
XHTML elements and attributes must be lowercase as per XML conventions. Benefits include:
Avoids confusion between similar elements like <img> and <IMG>
Ensures consistent parsing across XML processors
Improves code readability and maintainability
Makes debugging simpler compared to arbitrary case
Enables interoperability with other XML languages
Non-compliance causes errors since XHTML interprets <IMG> and <img> as different elements.
13. How would you convert an HTML document to XHTML?
To convert to XHTML:
Declare XHTML doctype
Use lowercase for tags/attributes
Quote attribute values
Close all tags properly
Replace empty elements like <br> with <br />
Nest elements correctly
Include xmlns attribute in <html> tag
Validate with W3C Markup Validation Service
This ensures XHTML compliance. Legacy elements like <font> may need cleanup.
14. What challenges exist in migrating sites from HTML to XHTML?
Migrating from HTML to stricter XHTML can pose challenges like:
Rewriting sloppy markup with missing tags or quotes
Fixing capitalization errors for compliance
Ensuring proper nesting of elements
Adding slashes to self-closing tags
Testing for and resolving functional breaks
Planning the migration by auditing the codebase helps. Legacy HTML can make full migration difficult in some cases.
15. How do you handle browser compatibility issues in XHTML?
To maximize compatibility:
Validate markup using W3C tools to avoid non-standard code
Use proper XHTML DOCTYPE to trigger standards mode
Incorporate CSS resets like Normalize.css for consistency
Ensure JavaScript degrades gracefully without support
Test extensively across different browsers and platforms
Use feature detection and polyfills for advanced functionality
Progressive enhancement ensures critical functionality works everywhere.
16. How can you improve accessibility in XHTML?
Some tips for accessible XHTML:
Use semantic elements like <header>, <nav>, <main>
Provide textual alternatives via alt attributes
Associate labels to form controls
Ensure keyboard navigation is possible
Use ARIA roles appropriately
Follow color contrast standards
Size content relatively for text resize
This benefits users with disabilities through enhanced markup structure.
17. What is the proper way to handle empty elements in XHTML?
Empty elements like <br>, <hr>, <img> must use trailing slash syntax in XHTML e.g.:
This self-closing form enables valid XML parsing. Omitting the closing slash will break well-formedness.
18. What is the purpose of XHTML Modularization?
XHTML Modularization allows mixing and matching XHTML modules to build custom markup languages targeted for specific devices or applications.
Benefits include:
6 Answers 6 Sorted by:
Bugs in validation don’t make downloads take longer; in fact, the only thing that keeps it from being valid HTML 4 is some extra whitespace. 01 Transitional is the missing alt attribute).
The things that could increase download times are:
They might be bigger than 10×10 and need to be shrunk down.
Instead of cache-friendly CSS, presentational attributes are used, which won’t make a difference for this one time.
Since links inside other links have a border by default, border=0 might not be as “unnecessary” as you think (though it is still better to use CSS for this).
There is a space at either end. Thats 2 unnecessary bytes to download 😉
something.gif might not actually be pointing to a static picture on the filesystem.
Reduces the download time by about one round trip time. Since its quite small, 10 by 10, the overhead of base64 is not significant, I think.
The code is very big, which is why it takes longer to load or show.
The is using a relative path, so it might not download at all if you look at it in an email client.
XHTML Interview Questions and Answers
FAQ
What is the main goal of XHTML?
The primary goal of XHTML is to create a stricter way to develop websites consistently and expectantly. XHTML works by allowing you to write standard HTML using the strict guidelines of the XML format.
What is XHTML short answer?
XHTML (Extensible HyperText Markup Language) is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML) Flexible framework requiring lenient HTML specific parser. Restrictive subset of XML which needs to be parsed with standard XML parsers.
What is the difference between HTML and XHTML?
HTML (HypertextMarkup Language) and XHTML (ExtensibleHypertext Markup Language) are both markup languages used for creating and displaying web pages. The main difference between them is the syntax and structure; HTML is more lenient in its syntax, while XHTML has a more strict syntax and follows XML rules.
What are HTML interview questions?
We’ve divided these questions into beginner, intermediate and advanced level HTML interview questions. 1. Define HTML. HTML stands for HyperText Markup Language. HTML is a standard text formatting language that creates and displays a variety of pages on the web. 2. What are the components of HTML?
Why is XHTML better than HTML?
All XHTML elements must always be closed. All XHTML elements must be written in lower case. Every XHTML document must have one root element. That is the reason behind its preferences over HTML because; most of the web pages contain bad HTML. 3) What is the difference between XHTML and HTML?
What attributes are used in HTML interview questions?
Style, class, and id are the commonly used attributes. span element: The span element is used as a container for text. It has no required attributes. Style, class, and id are the commonly used attributes. HTML Interview Questions contains list of most frequently asked in interviews questions and answers.
Which XML tags must be nested?
The xmlns attribute in is mandatory and must specify the xml namespace for the document. ,
