Google Mail or Gmail provides developers with an extensibility model in the form of Gmail gadgets. Gmail gadgets come in two flavors: Sidebar gadgets and contextual gadgets.
Sidebar gadgets are shown on the left hand side of the Gmail user interface, just underneath the list of folders – this can be compared to setting your Add-in Express Advanced Task pane’s ExplorerLayout property to BottomNavigationPane.
Contextual gadgets are gadgets that run when certain clues are detected in Gmail. This can be a based on text in the subject or in the message body. For example the translate gadget in Gmail is automatically shown when a foreign language is detected.
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