Was bedeutet dieser Android-Code?

Was ist der Unterschied zwischen* ,+ und leer:

@*android:id

so in android_ics / packages / apps / Setting / res / layout

<TextView android:id="@*android:id/timeDisplayForeground"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:singleLine="true"
    android:ellipsize="none"
    android:textSize="@dimen/crypt_clock_size"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:textColor="@color/crypt_keeper_clock_foreground"
    android:layout_alignLeft="@*android:id/timeDisplayBackground"
    android:layout_alignTop="@*android:id/timeDisplayBackground"
    android:layout_marginBottom="6dip" />