Unavailable HTML elements are used in the form template.

Some HTML elements are not permitted to be used in the form template. You will be warned by this message when the config-validator detects uses of unavailable HTML elements.

A typical example of an unavailable HTML element is the <form> element. Because Contact Form 7 moves the content of the form template into a <form> element, and according to the HTML specification a <form> element is not allowed to be nested inside another <form> element, use of <form> elements in the form template make the HTML markup invalid and can lead to severe issues.

Just another contact form plugin for WordPress. Simple but flexible.