Layouts
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 - Provide the outermost HTML structure of a page.
 - There is **one** layout (per device) per page.
 - Apply to WebForms (.aspx) **and** MVC (.cshtml)
 - Comprise of Layout definition item and aspx page (WebForms) or cshtml file (MVC)

Sublayouts
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 - Provide inner HTML structure to a component or structuring element of a page.
 - Apply only to WebForms 
 - Comprise of a definition item + .ascx control.
 - Can contain nested Sublayouts within their placeholders

Renderings
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 - Provide inner HTML structure to a component or structuring element of a page.
 - Can be used with WebForms OR MVC (if using XSLT)
 - Comprise of a definition item + .xslt or .cshtml view
 - Can contain nested renderings (or sublayouts [1]) within their placeholders
 

[1] can only contain nested sublayout if xslt rendering within a WebForms solution