HTML Guide

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 value of the maxlength attribute contains invalid characters because it is incorrectly combined with another attribute.

In HTML, the maxlength attribute for an input element should contain only a non-negative integer value, which specifies the maximum number of characters allowed in the input. The aria-required attribute must be a separate attribute in the tag.

Correct usage separates each attribute and assigns the appropriate value using quotation marks for each. For example, maxlength="200" and aria-required="true" must be distinct and not combined.

Incorrect:

<input type="text" name="nome" id="nome" maxlength="200 aria-required="true">

Correct:

<input type="text" name="nome" id="nome" maxlength="200" aria-required="true">

This valid example uses maxlength="200" for character limit and adds aria-required="true" to improve accessibility for assistive technologies.

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 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.

type="datetime" is obsolete; it was removed from HTML and is not valid in modern browsers or validators.

Explanation

The input element’s type attribute accepts specific keywords defined by the HTML Living Standard. The keyword datetime was dropped; use either:

• type="datetime-local" for a local date and time without timezone.
• type="date" or type="time" when collecting them separately.
• type="text" with a pattern or a JS widget when timezone-aware datetime is required.

Relevant attributes that still apply include name, value, min, max, and step (e.g., seconds for datetime-local).

HTML examples

Example reproducing the error

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Invalid input type</title>
</head>
<body>
  <form>
    <label>
      Meeting:
      <input type="datetime" name="meeting">
    </label>
  </form>
</body>
</html>

Valid fix with datetime-local

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid input type</title>
</head>
<body>
  <form>
    <label>
      Meeting:
      <input type="datetime-local" name="meeting" step="60">
    </label>
  </form>
</body>
</html>