uPortal Layout Loading & Transformation
Layout DOMs are loaded through a layout manager interface which hides the details as to how the resulting DOM is constructed. The DOM is transformed twice, once by the structure transform and a second time by the theme transform.
The layout DOM uses a very abstract concept of <folder> elements as nodes and <channel> elements as leaves to describe the entire layout of the user. These elements have attributes added by the layout manager to describe their function, rules and some behavior. The guestLayout.xml and adminLayout.xml attachments are examples of raw layout documents from uPortal 2.6. The structure transform works on the layout DOM to create the structure DOM.
The structure DOM describes the structure of the current view of the portal user's layout. The abstract folder/channel structure is transformed into a more concrete structure. There is no set requirement for the format of the structure DOM but there are very few instances of this format being changed. The default structure DOM consists of header, footer, navigation, content, columns and channels and this format is simply an agreement between the output of the structure transform and the expected input of the theme transform. The guestStructure.xml and adminStructure.xml attachments are examples of post-structure transform documents from uPortal 2.6. The theme transform works on the structure DOM to generate the content rendered to the user (generally HTML).