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The single-page complex form allows to fill in larger amounts of data and replaces the existing form with horizontal tabs. The main characteristic of this form is that it provides an instant overview over all key values, even those contained in other tabs (see also the explanation below).
The data sets the form collects are organized using vertical tabs to make the forms wider than high. Inside a single form, the fields used to obtain the actual data can be grouped using various grouping elements such as blocks and field sets. In fact, the single-page complex form builds on the same principles as the standard form and also uses the same mechanisms to show notification messages.
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Properly structuring and arranging form elements is often a UX task, but one that should be somewhat straight forward in this case, if you have a clear understanding of the type and structure of your data and use the grouping elements described above according to their intent. Try to place all mandatory values into the first form of the first tab. The idea is that these important fields pop up immediately as soon as the form shows up. In a typical case, I would only have to look at the first form, fill in values there, glance over the summary texts of the other tabs to verify if the defaults match my expectations, and if they do, click save. I should not have to click through every tab sequentially once I'm accustomed to a form and don't have any extra requirements.
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