<uses-sdk> string values

[Eom]

I was inspecting the content of sailfish-opp2.170420.019's system.img, and I noticed some weird stuff.

According to the official documentation at https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#max the values of android:minSdkVersion, android:targetSdkVersion and android:maxSdkVersion are expected to be an integer.

And yet, /system/app/UserDictionaryProvider/UserDictionaryProvider.apk and /system/app/WallpaperBackup/WallpaperBackup.apk Manifest files does not meet this standard, 

<?xml version="1.0" encoding="utf-8"?>
<manifest android:sharedUserId="android.uid.system" android:versionCode="25" android:versionName="O" package="com.android.wallpaperbackup" platformBuildVersionCode="25" platformBuildVersionName="O" xmlns:android="http://schemas.android.com/apk/res/android">
    <uses-sdk android:minSdkVersion="O" android:targetSdkVersion="O" />
    <application android:allowBackup="true" android:allowClearUserData="false" android:backupAgent=".WallpaperBackupAgent" android:backupInForeground="true" android:fullBackupOnly="true" android:killAfterRestore="false" android:process="system" />
</manifest>

As you can see here: <uses-sdk android:minSdkVersion="O" android:targetSdkVersion="O" /> the values of android:minSdkVersion and android:targetSdkVersion are strings and not integers.

Is this a bug? A new undocumented feature?