HTML Guide

The autocomplete attribute is used to control if the browser can provide assistance in filling out form field values, and it only makes sense for visible, not hidden, inputs.

It is available on <input> elements that take a text or numeric value as input, <textarea> elements, <select> elements, and <form> elements.

To fix this issue, you can remove the autocomplete attribute from the input element with type=hidden. Here is an example:

<!-- Wrong code -->
<input type="hidden" name="phone" value="12345" autcomplete="off">

<!-- Correct code -->
<input type="hidden" name="phone" value="12345">

The aria-* attributes are part of the WAI-ARIA (Web Accessibility Initiative-Accessible Rich Internet Applications) suite. They are used to improve the accessibility of web pages. However, when we use an input element with a type attribute whose value is hidden, we imply that the element is invisible and has no interaction with the user. Therefore, it doesn’t make sense to add aria-* attributes to it.

To fix this issue, you need to remove the aria-* attributes from the input element with type=hidden. Here is an example:

<!-- Wrong code -->
<input type="hidden" name="referer" value="https://example.com" aria-invalid="false">

<!-- Correct code -->
<input type="hidden" name="referer" value="https://example.com">

When nesting an input element inside a label that has a for attribute, the id attribute of the input is required to match it.

The label element represents a caption in a user interface. The caption can be associated with a specific form control, known as the label element’s labeled control, either using the for attribute, or by putting the form control inside the label element itself.

When the input is inside the label, there’s no need to specify a for attribute as there can only be one input, as in this example:

<label>
  Age
  <input type="text" name="age">
</label>

However, if the for attribute is specified, then it must match the id of the input like this:

<label for="user_age">
  Age
  <input type="text" name="age" id="user_age">
</label>

The maxlength attribute can be used on an input element to define a client-side validation for the maximum length allowed on an input without resorting to JavaScript.

This attribute is only allowed on elements of type email, password, search, tel, text, or url.

The minlength attribute can be used on an input element to define a client-side validation for the maximum length allowed on an input without resorting to JavaScript.

This attribute is only allowed on elements of type email, password, search, tel, text, or url.

The minlength attribute defines the minimum number of characters (as UTF-16 code units) the user can enter into an <input> or <textarea>. This must be an integer value 0 or higher. If no minlength is specified, or an invalid value is specified, the input has no minimum length. This value must be less than or equal to the value of maxlength, otherwise the value will never be valid, as it is impossible to meet both criteria.

Here’s an example:

<label for="name">Enter your name (max 25 characters)</label>
<input type="text" minlength="25" id="name">

The pattern attribute is only allowed on input whose type is email, password, search, tel, text or url. Check the type used, and consider changing to one of the allowed types to enable pattern client-side validation.

The pattern attribute is a handy way of adding client-side validation on HTML forms without resorting to JavaScript. Check out this article to learn more about Input Pattern.

The step attribute is a number that specifies the granularity that the value must adhere to.

It sets the stepping interval when clicking up and down spinner buttons, moving a slider left and right on a range, and validating the different date types.

When used, it must be greater than zero.

Example:

<form>
  <!-- Valid values include 1.3, 3.3, 5.3, 7.3, 9.3, 11.3, and so on -->
  <input id="myNumber" name="myNumber" type="number" step="2" min="1.3" />
</form>

The role attribute value combobox is not valid on an input element according to the W3C HTML standard.

The role="combobox" is valid only when applied to an element that acts as a container for the combo box widget, usually a div or similar element, and not directly to a native HTML input. Native input elements of type "text" or "search" already have implicit roles and accessibility semantics. To create an accessible combobox, wrap the input inside a container element with role="combobox" and use appropriate ARIA attributes.

Incorrect Implementation:

<input type="text" role="combobox" aria-autocomplete="list">

Correct Implementation:

<div role="combobox" aria-haspopup="listbox" aria-owns="suggestions" aria-expanded="false">
  <input type="text" aria-autocomplete="list" aria-controls="suggestions">
</div>
<ul id="suggestions" role="listbox">
  <li role="option" id="option1">Option 1</li>
  <li role="option" id="option2">Option 2</li>
</ul>

Explanation of attributes:

• role="combobox": Applied to the container (<div>) to define the accessible widget.
• aria-haspopup="listbox": Indicates the presence of a list of suggestions.
• aria-owns / aria-controls: Connects the input and suggestion list.
• aria-expanded: Denotes whether the suggestion list is visible.
• aria-autocomplete: Defines the autocomplete behavior.

This markup ensures better accessibility and passes W3C validation.

The type dob is not valid for an input. If you want to build a date picker field, you can use the native HTML input elements with type date, datetime-local, or a generic text input decorated with JavaScript and CSS.

In HTML, the type attribute for the <input> element specifies the type of input control that is to be displayed. The type attribute can have values like text, password, email, date, etc. Using an unsupported or invalid value like dob (which presumably stands for “date of birth”) will cause this validation error.

Here’s an example of how you can correct this issue by using a supported type attribute value for the date of birth input:

<label for="dob">Date of Birth:</label>
<input type="date" id="dob" name="dob">

In this corrected example, we’ve used the type="date" attribute value for the date of birth input. This is a valid type for handling dates in HTML forms. Replace the input type with a supported type according to the specific data you need to capture.

Alternatively you can use a JavaScript library to build a date picker on a generic text input. For example, the popular bootstrap-datepicker library will generate a date picker around a text input.

The issue here is related to the encoding of URLs. In HTML and URLs, special characters that have specific meanings need to be encoded to ensure that the URL is interpreted correctly. This process converts characters to their percent-encoded form, where a character is replaced by % followed by two hexadecimal digits representing the ASCII code of the character.

Explanation:

• The action attribute of a <form> element specifies where to send the form-data when a form is submitted.
• If the URL contains special characters (e.g., spaces, <, >, #, %, etc.), they need to be percent-encoded. For instance, a space character is encoded as %20.
• In this case, the validator is complaining about a % sign that is not correctly followed by two hexadecimal digits, which typically happens if the URL was not properly encoded.

How to Fix:

1. Check the URL: Look for any raw special characters that need encoding.
2. Correctly Encode the URL: Use online tools or libraries that provide URL encoding support to ensure that the URL is correctly percent-encoded.

Example:

Suppose you have the following incorrect form tag:

<form action="submit%data.html">
  <!-- form elements here -->
</form>

The % in submit%data.html should be followed by two hexadecimal digits. If %data was intended to be a part of the URL, it should be encoded properly. Here is how to correct it:

<form action="submit%25data.html">
  <!-- form elements here -->
</form>

If % should represent data, replace % with %25, which is the percent-encoded form of %. Always verify each special character is correctly encoded. Using this approach ensures that the URL in the action attribute is valid according to HTML standards.