What element adds a caption to the top of a fieldset in a form?

The addition of a caption to the top of a fieldset in a form is done using the legend element. This element is specifically designed for this purpose, providing a semantic way to describe the grouping of related form controls contained within the fieldset. When a legend is used, it visually represents a heading or title for the fieldset, helping users understand the context of the inputs below it.

This element not only enhances the accessibility of the form for users but also improves the overall user experience by providing clear labeling. The legend element is often rendered in a distinct style, making it stand out and easily identifiable as the title of the fieldset. In contrast, other elements do not serve this specific function within the context of a form.