Explain Structure
Structure is the core of your page. You build the walls, roof and stairs with structure.
Page
Purelly HTML5, without page the exported file is not HTML. All other content will be added inside the page.
Grid System
POSHTML5 use grid system of PicoCSS Framework. The page is divided in to axes: X (rows) and Y (Columns). Each row could contains mutiple columns. Column's width is auto-sized, 100% of page width divided by number of columns. You could refer to it for more details.
Tabs
Use Tabs to create multiple pages on a single page and better organize your report. Tabs can contains what you want, like a classic page. Tab don't replace Page but they works together.
HorizontalScroller
Use it to shrink a large object and a on it a scroller.