alt+shift+down selects larger or smaller portion of the AST. It allows for quick selection of sub-expressions or statements.
Shortcuts are platform-dependent, and can be re-configured in the
Keys preference page. The actions are named Select Enclosing Element and Restore Last Selection.
Hovering over the selection will also bring up a dialog dispaying the inferred type of the selected expression, just as it would if you put the cursor on a specific element.