Clarify docs for custom form structure

Fixes twbs#25440

Author: mdo

site/docs/4.1/components/forms.md

@@ -1105,7 +1105,7 @@ For even more customization and cross browser consistency, use our completely cu
 
 ### Checkboxes and radios
 
-Each checkbox and radio is wrapped in a `<div>` with a sibling `<span>` to create our custom control and a `<label>` for the accompanying text. Structurally, this is the same approach as our default `.form-check`.
+Each checkbox and radio `<input>` and `<label>` pairing is wrapped in a `<div>` to create our custom control. Structurally, this is the same approach as our default `.form-check`.
 
 We use the sibling selector (`~`) for all our `<input>` states—like `:checked`—to properly style our custom form indicator. When combined with the `.custom-control-label` class, we can also style the text for each item based on the `<input>`'s state.