Moves the cursor to the most base structure type of the selected variable or type. For example, consider the following code:
// MS type is defined as struct MyStruct
typedef struct MyStruct MS;
MS ms; // declare ms with a type of "MS"
x = ms.afield;
If you put the cursor in ms in the assignment statement (or anywhere the ms variable appears), the Jump To Base Type command will jump to the definition of struct MyStruc, because that is the most base structure type of the variable. It won't stop at the typedef of MS.