Magento Go, our SaaS solution, provides merchants with capabilities to customize their stores with different themes and to integrate applications for valuable functionality. We will provide examples of the best methods and approaches for customizing storefronts with different themes and layouts, as well as how to integrate apps into Magento Go stores.
Layout is actually a hierarchical tree of all visual blocks that form visual appeal for a page. It's obvious that some elements are meant to be displayed on every page and some of them — on specific pages only. Magento recognizes several cases like this and supports specific layouts for every case.
Block - Is used to create a new block in current context. Layout block nesting defines the ordering of block initialization location of the blocks on the page.
Reference - Changes the context for all included instructions to a previously defined block. Empty <reference> tag makes no sence, it affects only instructions which are children
Action - Is used to access block API, in other words, call block's public methods. It is used to set up the execution of a certain method of the block during the block generation. Action child tags are translated into block method arguments. The list of all available methods, depends on the block implementation (e.g. public method of the block class).
Remove - Is used to remove an existing block from the layout.