Despite the placement of "thead" and "tfoot" in your HTML code, visually, browsers always render "thead" at the top and "tfoot" at the bottom of the table. This ensures that header and footer information is consistently displayed in the correct locations, even if the code sequence differs. 

The tabindex attribute in HTML specifies the tab order of an element. A positive value ensures the element is focusable in sequential keyboard navigation. It's particularly important for making interactive elements accessible to keyboard users. If an element should be focusable but not in the sequential keyboard flow, tabindex="0" can be used. 

The
tag is an HTML element used to insert a line break, which ends the current line and tells the browser to start a new line. It's especially useful within text content like a paragraph (

) where you might want to create a break without starting a new paragraph. The
tag is an empty tag, meaning it doesn't have a closing tag. 

Implementing CSS Grid or Flexbox for layout management is a modern approach to design responsive web layouts. These techniques allow for fluid grid systems, which adapt to varying screen sizes without requiring separate designs for each size. Fixed widths are not responsive, designing different versions for each screen size isn't scalable or efficient, and adding more pages doesn't directly address responsiveness. 

Comments in HTML are primarily used as a tool for developers. They allow coders to leave notes, explanations, or annotations within the code, helping to make the code more understandable and maintainable for other developers who might work on the same project. While comments don't impact the display or functionality of a webpage, they are invaluable for teamwork and understanding the logic behind specific code sections. 

The white-space CSS property determines how white spaces inside an element are handled. By default, it's set to normal, which allows white spaces to collapse and line breaks to occur. However, if you want to control the line-breaking behavior of an inline element (like preventing it from breaking), you can use values like nowrap for the white-space property. 

The figcaption element is typically used with the

element to provide a caption or a reference for content such as

, images, or diagrams. When a blockquote needs additional context or a citation that isn't part of the quoting sentence, wrapping the blockquote in a

and using a

To make tables responsive, especially for mobile views where screen real estate is limited, the display: block; property can be employed. This takes the table out of its default table display context and makes it behave like a block-level element. This is often combined with media queries and other techniques to stack rows or reformat the table structure for better mobile readability. 

The

tag is used to provide a title or a summary for an HTML table. It helps give context and improve the accessibility of the table by informing users about the table's content or purpose at a glance. Typically, the caption will be centered above the table. 

Using Flexbox is one of the modern approaches to layout designs and is very effective in spacing elements evenly within a container. By setting the container to display: flex; and using justify-content: space-between;, you can ensure that the inline elements (like navigation links) are spaced evenly. Additionally, Flexbox is responsive by nature, allowing for adjustments based on different viewport sizes.