docs(input) more descriptive fixed text documentation

ui/components/input/_doc.scss

@@ -20,10 +20,6 @@
  * If the error message has an `id="my-error-message"`, then the input should
  * have `aria-describedby="my-error-message"`.
  *
- * ##### Fixed Text
- *
- * When using the fixed text variants for prepending or appending symbols to inputs, please be sure to use `aria-labelledby` on the input, that points to the ids of the label, prepended text and appended text as a space separated list. The IDs must appear in that order, label, prepended, then appended.
- *
  * If you need some type of field level help and if your tooltips are
  * available on hover, make sure they’re also available on keyboard focus. The
  * help icon needs to be associated to the tooltip so that when the user focuses
@@ -33,6 +29,19 @@
  *
  * In some cases, the read-only field state is swapped and has no `<input>`. This is called `static` in the examples. In that case, don’t use a `<label>`. This provides better accessibility for screen readers and keyboard navigators. Instead, use a `<span>` with the `.slds-form-element__label` class. Instead of an `<input>`, use the `.slds-form-element__static` class inside the `.slds-form-element__control` wrapper.
  *
+ * ##### Fixed Text
+ *
+ * When using the fixed text variants for prepending or appending symbols to inputs,
+ * please be sure to use `aria-labelledby` on the input, that points to the ids of the label,
+ * prepended text and appended text as a space separated list. The IDs must appear in that order:
+ * label, prepended, then appended.
+ *
+ * The reason we do this is to create a better association between the input and the supporting labels around it.
+ * By only using the traditional `label[for]` method, the fixed text is never read out in the context of editing
+ * the input value. With using the `aria-labelledby` attribute we can create a better label with all the
+ * visual labels associated with it, in a relevant order, that is read by assistive technology when the user
+ * needs it; when they're editing the value.
+ *
  * @summary Text inputs are used for freeform data entry
  *
  * @base