What is an XSL-FO block? XSL-FO output goes into blocks. Blocks of content flow into pages of the output media. XSL-FO output is normally nested inside <fo:block> elements, nested inside <fo:flow> elements and/or nested inside <fo:page-sequence> elements. Blocks are sequences of output in rectangular boxes, so they share many common area properties:
• space before and space after
• margin
• border
• padding
Space before and space after are the empty spaces separating the block from the other blocks.
Margin is the empty area on the outside of the block.
Border is a rectangle drawn around the external edges of the area. It may have different widths on all four sides and can also be filled with different colors and background images.
Padding is the area between border and content area.
The Content area contains the actual content like text, images and more.
Please see relevant technical XSL literature for details and further information, e.g. http://www.w3.org/TR/xsl or http://www.w3schools.com/xslfo/.