This article is about the different type of order of HTML element.
There is three kind of order:
The source order is order of the element in the html document from top to bottom.
This is the default order for the next type of order.
The visual order is the order as perceived by the eye
This order is determined by the CSS layout.
The principal order is given by how user would read the page.
Note that the visual display order may be different by screen sizes.
The tab order is the order of interactive element. You can loop through them via the tab key. This is particularly important for:
See What is the Tab Order (Keyboard focus navigation)