clarify

docs/4.0/components/input-group.md

 ---
 layout: docs
 title: Input group
-description: Easily extend form controls by adding text, buttons, or button groups on either side of textual inputs.
+description: Easily extend form controls by adding text, buttons, or button groups on either side of textual inputs, custom selects, and custom file inputs.
 group: components
 toc: true
 ---
 
+
+
 ## Basic example
 
 Place one add-on or button on either side of an input. You may also place one on both sides of an input. **We do not support multiple form-controls in a single input group** and `<label>`s must come outside the input group.