Even more detail: ”Creating a FastTab is easy. A FastTab is a group control directly within the content area of a card, document, or task page.”In the Content area of the hosting page, parts can only be collapsed if they satisfy the following rules:parts are hosted on a task dialog, card, or document page.parts aren't placed within a FastTab.”(1) This means that they have to be their own group and cannot be part of another group "When placing two ListParts in a group, they share horizontal space." (2) This is the only way to have parts side by side(1) + (2) = It’s impossible to have them side by side and also be collapsable/expandable. As for the actions issue: In the Content area of the hosting page, parts will only display an expanded action menu if they satisfy the following rules:parts are hosted on a card or document page.parts aren't placed within a FastTab.”Meaning again, that it's impossible to have them side by side and also have promoted actions.