Studio Build:
Version of Gradle Plugin:
Version of Gradle:
Version of Java:
OS:
Android Studio 3.3 Canary 10
Build #AI-182.4129.33.33.4996246, built on September 6, 2018
JRE: 1.8.0_152-release-1248-b01 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0

Steps to Reproduce:
0. Create project that has minSdk set to be low (15 for example).
1. Have a FrameLayout with some "foreground" set to it, in the layout xml file. Example:

<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent" android:layout_height="wrap_content"
android:foreground="?android:windowContentOverlay" />

2. Notice IDE shows warning that "foreground" is only available from API 23 . This is wrong, as it is supported much before API 23.
3. Try to see what the docs have to say about this:
https://developer.android.com/reference/android/widget/FrameLayout
https://developer.android.com/reference/android/view/ViewGroup
https://developer.android.com/reference/android/view/View#attr_android:foreground
https://developer.android.com/reference/android/view/View.html#setForeground(android.graphics.drawable.Drawable)

The bug here, is that there is no warning about this here. In fact it says it's from API 1.

Attached sample to test on various old Android devices. Use on older than API 21, to see that indeed it still works fine

Issue 115828845