Here are 7 lesser-known HTML features that can enhance your web development skills

1. <details> and <summary>:
   These elements create a disclosure widget that users can open and close. <details> is the container, and <summary> is the visible heading that users click to expand or collapse the content.

   <details>
     <summary>More Information</summary>
     <p>This content is hidden until the user clicks "More Information".</p>
   </details>

2. <datalist>:
   This element provides an autocomplete feature for input elements. It defines a list of predefined options for an <input> element.

   <input list="browsers" name="browser">
   <datalist id="browsers">
     <option value="Chrome">
     <option value="Firefox">
     <option value="Safari">
     <option value="Edge">
   </datalist>

3. <output>:
   This element represents the result of a calculation or user action. It’s often used with JavaScript to display dynamic values.

   <form oninput="result.value=parseInt(a.value)+parseInt(b.value)">
     <input type="range" id="a" value="50"> +
     <input type="number" id="b" value="100">
     = <output name="result" for="a b">150</output>
   </form>

4. <progress>:
   This element displays the progress of a task. It shows a progress bar indicating the completion percentage.

   <progress value="70" max="100">70%</progress>

5. <meter>:
   This element represents a scalar measurement within a known range, or a fractional value. It’s useful for displaying values such as disk usage or battery life.

   <meter value="0.7" min="0" max="1">70%</meter>

6. <template>:
   This element holds client-side content that won’t be rendered when the page loads but can be instantiated later using JavaScript. It’s useful for storing reusable content fragments.

   <template id="my-template">
     <div class="my-content">
       <h2>Template Content</h2>
       <p>This content can be cloned and inserted into the DOM.</p>
     </div>
   </template>

7. Custom Data Attributes (data-*):
   These attributes allow you to store extra information on HTML elements without using non-standard attributes or DOM properties. They can be accessed using JavaScript.

   <div data-user-id="12345" data-role="admin">User Info</div>
   <script>
     const userInfo = document.querySelector('[data-user-id]');
     console.log(userInfo.dataset.userId); // Output: 12345
     console.log(userInfo.dataset.role);   // Output: admin
   </script>