From FDT Documentation
If the cursor is placed on a literal - no matter, if it is a variable, a function or a class - using F3 makes the cursor jump directly to the declaration.
For example, In the case of a variable, FDT will jump to where the variable is defined - either at the top of the class or within the scope of a method. In the case of a type, FDT will open the Class in the editor.
Default binding is F3.