HTML & CSS - - By Aurelio De Rosa

10 Typical HTML Interview Exercises

A few weeks ago SitePoint published two of my articles discussing some commonly asked JavaScript job interview questions (in case you missed them, the articles are 5 Typical JavaScript Interview Exercises and 5 More JavaScript Interview Exercises).

Both these articles have been a huge success in terms of page views and shares, which was quite unexpected. So, I thought it was time to write a similar article based on job interview questions on HTML and this is the result of my effort. Have fun!

1. Markup validation

Consider the following markup:

<figure>
   <picture>
      <source media="(min-width: 40em)"
      srcset="large.jpg 1024w, medium.jpg 640w, small.jpg 320y">
      <img src="medium.jpg" alt="London by night">
   </picture>
   <figcaption>A landscape of London by night</figcaption>
</figure>

Is it valid? If not, can you explain why?

Answer

The markup uses the picture element, which is a pretty new addition to the specification. The code is all valid apart from the last image specified in the srcset attribute; 320y isn’t a valid value. If the y is replaced with a w, it becomes valid though.

2. The main element

Can you explain the definition of the main element? What is its goal? Are the two specifications (WHATWG and W3C) in agreement on its definition?

Answer

The main element has two different definitions depending on the specification used.

The W3C specification describes it as the main content of the page, that is, the content that describes the main topic of a page or is the central functionality of an application. The specification also states that a document must not include more than one main element.

The WHATWG specification doesn’t assign any semantic value to the main element and describes it as a container for the dominant contents of another element. Also, according to WHATWG, you don’t have a limit in the number of times you can use the main element in a single document. If you have multiple article elements on a page, you may want to markup the main content of each article with a separate main element.

3. WAI-ARIA

Consider the following snippet:

<header>
   <h1>Main title</h1>
   <form action="/" method="get">
      <input type="search">
      <input type="submit">
   </form>
</header>
<ul>
   <li><a href="/">Home</a></li>
   <li><a href="/products">Products</a></li>
   <li><a href="/about">About</a></li>
</ul>
<main>
   <article>
      <h1>Main title</h1>
      <p>This is the content of this section</p>
   </article>
</main>
<footer>
   <small>Copyright &amp;copy; Aurelio De Rosa 2014</small>
</footer>

Can you improve its accessibility using WAI-ARIA roles where appropriate, taking into account older technologies?

Answer

The code can be rewritten as follows:

<header role="header">
  <h1>Main title</h1>
  <form action="/" method="get" role="search">
     <label for="search">Search:</label>
     <input id="search" type="search">
     <input type="submit">
  </form>
</header>
<nav role="navigation">
  <ul>
     <li><a href="/">Home</a></li>
     <li><a href="/products">Products</a></li>
     <li><a href="/about">About</a></li>
  </ul>
</nav>
<main role="main">
  <article role="article">
     <h1>Main title</h1>
     <p>This is the content of this section</p>
  </article>
</main>
<footer role="contentinfo">
  <small>Copyright &amp;copy; Aurelio De Rosa 2014</small>
</footer>

To improve the accessibility, the main navigation list has been wrapped with a nav element. To improve the accessibility in older technologies that don’t support the new semantic elements, the role of header, navigation, main, article, and contentinfo have been added to the header, nav, main, article, and footer elements respectively.

Other improvements have been made on the search form. First of all the form has been marked using the search role. Then, an explicit label element has been added to give context for the input field, and it has been associated with the input through the use of the for attribute.

4. The small element

Describe when it’s appropriate to use the small element and provide an example.

Answer

In HTML 4.01 the small element was a presentational element to mark up smaller text. In HTML5 it should be used semantically to represent legal disclaimers, caveats, and so on. The text may well be “small”, but this isn’t required.

An example of its use is shown below:

<img src="image.jpg" alt="London by night">
<small>The copyright of this image is owned by Aurelio De Rosa</small>

5. Subheadings

Subheadings are one of the most common elements in any website. A few years ago the hgroup tag was introduced to address this need, but it has since been removed from the specs. Can you describe why hgroup was dropped and how the markup can be addressed today?

Answer

The hgroup element was introduced to group multiple heading elements (h1h6) in order to avoid the creation of an unintended sublevel in the hierarchy. To understand what problem it tried to address, let’s consider the following markup:

<article>
   <h1>Main title</h1>
   <h2>This is a subtitle</h2>
   <p>This is the content of this section</p>
</article>

Outlining the document hierarchy of the previous snippet gives us the following representation:

h1
|
---h2
   |
   p

This simple schema shows that the paragraph content of the snippet is seen as the content of the h2 instead of the h1, regardless if this was the intended behavior or not. So if the intention was simply to create a subheading and to associate the p with h1, the original markup was incorrect.

The hgroup element was introduced to address this issue with ease. Therefore, it was removed from the HTML5 specification in April 2013, due to lack of implementations and lack of use cases, making its use invalid.

A possible solution to create a subtitle so that the paragraph is associated to the h1 is shown below:

<article>
   <h1>
       Main title
       <span>This is a subtitle</span>
   </h1>
   <p>This is the content of this section</p>
</article>

6. Images and accessibility

Is the alt attribute mandatory on img elements? If not, can you describe a scenario where it can be set to an empty value? Does an empty value affect accessibility in any way?

Answer

The alt attribute is mandatory on img elements but its value can be empty (i.e. alt=""). An empty value is recommended when the image shown is used for decorative purposes only and therefore isn’t part of the content of the page. With regards to accessibility, if the alt attribute is empty, screen readers will ignore the image. This is highly recommended because using a value of something like “Content separator” will only disturb the user when this text is spoken.

7. The time element

Is it possible to express a date range using a single time element?

Answer

No, it isn’t possible. The information can be expressed using two time elements though. For example to describe a time interval ranging from November 6, 2014 to November 9, 2014, a developer can write:

<time datetime="2014-11-06">6</time>-
<time datetime="2014-11-09">9 November 2014</time>

8. meter and progress

What’s the difference between the meter element and the progress element?

Answer

The meter element represents a scalar measurement within a known range, or a fractional value. This element isn’t a good fit to measure something like external temperature because it doesn’t have a fixed range. However, meter can be used to describe the occupied memory of a hard disk.

The progress element is used to show the completion progress of a task. Unlike the meter element, the progress described by progress can be indeterminate. For example you could describe that a given task is progressing but that it is unknown when the task will be completed.

9. The longdesc attribute

What is the longdesc attribute? Can you explain its purpose?

Answer

The longdesc attribute of the img element has been around since HTML 4 and is also valid in HTML5. This attribute is designed to provide a more detailed description of an image, compared to the information offered in the alt attribute. The interesting thing is that instead of providing a description by itself (like the alt attribute does), longdesc points to a hyperlink containing the description.

An example of the use of longdesc is presented below:

<img src="italy.jpg"
     alt="This image represents the map of Italy" longdesc="italy.html#description">

<!-- other content here ... -->

<section id="description">
  <h2>Italy</h2>
  <p>The shown map of Italy illustrates its division 
  in regions...</p>
</section>

10. The mark element

What is the mark element? Can you describe an example of use for this element?

Answer

The mark element represents highlighted text. A typical use is to highlight every instance of the keyword or keywords searched by a user.

Conclusion

In this article I’ve discussed ten potential interview questions that you can use to test your knowledge of HTML. The questions you may be asked in your next interview may include one or more of these.

To help you study up on these and other semantics-related topics, be sure to check out the links provided in the article to the spec, and here are some further SitePoint resources:

Have you been asked some other interesting HTML questions in interviews? Share them with us, they may help other developers when doing interviews for positions in the future.

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