XHTML Block
An XHTML block is a reusable block of content that provides a rich WYSIWYG interface for editing content. Unlike the text block counterpart, an XHTML block allows for a wide range of HTML elements to be created inside of its editing environment extending to items such as images, links, tables, and bullet points in addition to other standard text formatting.
XHTML blocks are particularly useful for fixed regions of content such as headers and footers that need to stay constant among all pages within the site. A single change to one of these blocks will be present across all pages of the site that make use of the block. The basic level of modularity improves the scalability of the website in addition to allowing for easier "quick edits" that cannot be easily performed if the content were to remain in the body of the overall template.
Additional Notes
Due to its inherent flexibility for content editing, it is possible that certain fixed-width/height pieces of content in an XHTML block (for example HTML tables) can affect the overall integrity of the template if they are sized to be larger than the allowed width of the content region. It is suggested, therefore, that only users with this understanding be given write access to XHTML blocks.