The code that controls the page layout and placement of blocks is written in XML. You might
have noticed references to XML Page Layout Updates throughout the Admin of your store.
Every product, category, and piece of content—whether it’s a page, block, or widget—has a
section where you can update the XML code that controls the positioning of the item. The
selection of available block references that is available varies by page type, and whether the
customer is logged in, or is visiting the as a guest.
Widgets make it easy to position a block at a specific place on the page, and even for a specific
product or category. You can select each option from a list, rather than trying to remember all
of the possible combinations.