HTML Guide
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 placeholder attribute is used on <input> elements as text that appears in the form control when it has no value set. Only inputs of type email, number, password, search, tel, text, or url accept this attribute.
For example, an input of type hidden doesn’t accept a placeholder attribute as it makes no sense to specify text to appear when the input is empty, if that input is hidden.
The boolean required attribute can only be used with certain types of inputs. Check the input type is one of the allowed.
The required attribute, if present, indicates that the user must specify a value for the input before the owning form can be submitted.
The seamless attribute was proposed to be included in the HTML5 spec, but it wasn’t finally accepted, so it’s not a valid attribute for <iframe>.
The attribute st_title is not allowed on <span> elements.
This issue is commonly caused by an old integration of ShareThis via Drupal or other CMS - the old code used invalid attributes like displayText, st_url and st_title which were later changed to HTML5 custom data attributes.
The attribute st_url is not allowed on <span> elements.
This issue is commonly caused by an old integration of ShareThis via Drupal or other CMS - the old code used invalid attributes like displayText, st_url and st_title which were later changed to HTML5 custom data attributes.
The <textarea> element does not have a type attribute.
The HTML <textarea> element represents a multi-line plain-text editing control, and is useful when you want to allow users to enter a sizeable amount of free-form text, for example a comment on a review or feedback form.
There is no attribute validate on the <form> element. Perhaps you meant novalidate?
If the novalidate attribute is present on a <form>, indicates that the form is not to be validated during submission.
For example, while this form has a required attribute on its input, it won’t be enforced because form validation has been disabled using novalidate:
<form novalidate>
<label>City: <input required name="city"></label>
<input type="submit" />
</form>
An attribute has been found in an element, where the intended value is missing. A common cause is including the equal sign, but not passing anything after it.
For example:
<!-- This is missing the value for the style attribute, so it's invalid -->
<p style=></p>
<!-- This is explicitly passing a blank string as the value, so it's valid -->
<p style=""></p>
Both xmlns:fb and xmlns:og attributes have been deprecated. If you’re using Facebook / Open Graph Protocol proprietary tags in you document, you can update the markup to the new syntax.