Document breaking change from #24932

docs/4.0/migration.md

@@ -14,6 +14,7 @@ While Beta 2 saw the bulk of our breaking changes during the beta phase, but we
 - Changed the CSS for managing multiple `background-image`s on custom form checkboxes and radios. Previously, the `.custom-control-indicator` element had the background color, gradient, and SVG icon. Customizing the background gradient meant replacing all of those every time you needed to change just one. Now, we have `.custom-control-indicator` for the fill and gradient and `.custom-control-indicator::before` handles the icon.
 - The npm package no longer includes any files other than our source and dist files; if you relied on them and were running our scripts via the `node_modules` folder, you should adapt your workflow.
 - Updated selector for input-based button groups. Instead of `[data-toggle="buttons"] { }` for style and behavior, we use the `data` attribute just for JS behaviors and rely on a new `.btn-group-toggle` class for styling.
+- Removed `.col-form-legend` in favor of a slightly improved `.col-form-label`. This way `.col-form-label-sm` and `.col-form-label-lg` can be used on `<legend>` elements with ease.
 
 ## Beta 2 changes