Android Studio XML 有小黄方块

Question

I think this little square means something important but don't know what... It goes away if I double click on it, but doesn't show up on less complex layouts within my project... any ideas why it's showing or what it means?

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/darker_gray"
android:orientation="vertical">

<android.support.v7.widget.Toolbar
    android:id="@+id/preferences_dialog_toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:minHeight="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">


    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Toolbar Title"
        android:textSize="30sp" />

</android.support.v7.widget.Toolbar>
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingTop="5dp"
    android:paddingBottom="5dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Options:" />

    <RadioGroup
        android:id="@+id/dataInputPreferenceRadioGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:gravity="center"
        android:orientation="horizontal">

        <RadioButton
            android:id="@+id/defaultUseInput"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:checked="false"
            android:text="Option1" />

        <RadioButton
            android:id="@+id/defaultUseTimeWidgets"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:checked="true"
            android:text="Option2"
            android:visibility="gone"/>
        <RadioButton
            android:id="@+id/defaultUseOption3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:checked="true"
            android:text="Option3" />
    </RadioGroup>
</LinearLayout>

Answer 1

I believe the little yellow square indicates a view that is hidden by being made invisible or gone.

Looking into this further, it only appears to indicate gone, not invisible.