Returns the innermost element within which this element is, loosely speaking, enclosed.

If this element is one whose declaration is lexically enclosed immediately within the declaration of another element, that other element is returned.
If this is a top-level type, its package is returned.
If this is a package, its module is returned if such a module exists. Otherwise, null is returned.
If this is a type parameter, the of the type parameter is returned.
If this is a method or constructor, the executable which declares the parameter is returned.
If this is a module, null is returned.

Returns: the enclosing element, or null if there is none