You may have seen an extra namespace, xmlns:tools="http://schemas.android.com.tools", in layout files generated by Android Studio. Adding this namespace to your layout provides you access to attributes, the Tools Attributes, that add metadata to resource files, that facilitate manipulating, rendering, and testing layouts in Design view, and (while I do not condone excess of this kind of behavior) that suppress certain Lint warnings (but only if you have a good reason for ignoring them, she nags). 

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