Docs: enhance floating labels placeholder usage description

Author: julien-deramond

site/src/content/docs/forms/floating-labels.mdx

@@ -6,7 +6,11 @@ toc: true
 
 ## Example
 
-Wrap a pair of `<input class="form-control">` and `<label>` elements in `.form-floating` to enable floating labels with Bootstrap’s textual form fields. A `placeholder` is required on each `<input>` as our method of CSS-only floating labels uses the `:placeholder-shown` pseudo-element. Also note that the `<input>` must come first so we can utilize a sibling selector (i.e., `~`).
+Wrap a pair of `<input class="form-control">` and `<label>` elements in `.form-floating` to enable floating labels with Bootstrap’s textual form fields.
+
+A non-empty `placeholder` attribute is required on each `<input>` as our CSS-only floating label implementation relies on the `:placeholder-shown` pseudo-element to detect when the input is empty. The placeholder text itself is not visible; only the `<label>` is shown to users.
+
+Also note that the `<input>` must come first so we can utilize a sibling selector (i.e., `~`).
 
 <Example code={`<div class="form-floating mb-3">
     <input type="email" class="form-control" id="floatingInput" placeholder="name@example.com">
@@ -49,7 +53,7 @@ To set a custom height on your `<textarea>`, do not use the `rows` attribute. In
 
 ## Selects
 
-Other than `.form-control`, floating labels are only available on `.form-select`s. They work in the same way, but unlike `<input>`s, they’ll always show the `<label>` in its floated state. **Selects with `size` and `multiple` are not supported.**
+Other than `.form-control`, floating labels are only available on `.form-select`s. They work in the same way, but unlike `<input>`s, they'll always show the `<label>` in its floated state. **Selects with `size` and `multiple` are not supported.**
 
 <Example code={`<div class="form-floating">
     <select class="form-select" id="floatingSelect" aria-label="Floating label select example">