HTML comments can contain special characters; however, they cannot include the character sequence "--" (double hyphen) as it signifies the end of the comment. Including "--" within a comment might cause the comment to terminate prematurely or result in a parsing error. 

The href attribute in the tag is used to specify the destination URL of the link. When creating a mail link, this attribute will have a value that starts with "mailto:" followed by the email address. For example, the attribute href="mailto:[email protected]" tells the browser to open the user's email client and populate the "To" field with "[email protected]". 

The

tag is suitable for block-level quotations, and within this tag, the

Search engines utilize meta tags primarily to gain insights into the content, structure, and relevance of a webpage. For instance, the 'description' meta tag might provide a brief summary that's displayed in search results, while the 'keywords' tag, although less influential now, was once used to understand the page's topics. It's a myth that meta tags directly boost a page's rank, but they can influence click-through rates from search results. 

Unordered lists (

) are commonly used for navigation menus due to their semantic and structural relevance. When styled with CSS, unordered lists can help represent menu items in a clear and visually organized manner, improving the user experience. They separate each menu item, making the structure clear to both visual users and assistive technologies like screen readers. This structured presentation ensures that the content is both accessible and easy to navigate. 

The

element, which stands for "table data", is used to define individual cells within a table row. Each

represents a unique cell, and its content can be text, images, or other elements. It's an essential part of constructing HTML tables, as it helps in arranging data into rows and columns. 

The

element stands for "table header". It's used to define a header cell in a table, providing emphasis to the content. Typically, content inside a

element is bold and centered. It's crucial for distinguishing column or row titles from the general data in a table, enhancing readability and providing context to the table's data. 

The reset button type creates a button that, when clicked, resets all the form fields to their initial values. This can be especially useful if a user wants to start over with the form. However, caution should be exercised with its use, as users might accidentally click it and lose all their input. 

The type attribute of the button element indicates the type of the button, such as "submit", "reset", or "button". It determines how the button behaves when it's clicked. For example, a "submit" type will submit the form data.