To include a predefined subject in an email link, you add ?subject= after the email address in the _____ attribute.

When creating an email link using the href attribute with a mailto: scheme, it's possible to add extra parameters to pre-fill various fields of the email. By appending ?subject= followed by the desired subject text, the email's subject line will be pre-filled with that text. For example, Email with subject will pre-fill the subject line with "Hello" when the link is clicked.