Document removal of deprecated screen size variables in the migration guide

diff --git a/docs/migration.md b/docs/migration.md
index dd3738c7b14144709dce093353765a8d38830fbc..c5416b6634cd61d8723a4901ea917d4b79a86607 100644 (file)
--- a/docs/migration.md
+++ b/docs/migration.md
@@ -51,4 +51,10 @@ The following components have been removed in v4.0.0.
 | Wells |  | Cards |
 | Justified navs | | |
 
+The following deprecated Less/SCSS variables have been removed in v4.0.0:
+* `@screen-phone`, `@screen-tablet`, `@screen-desktop`, `@screen-lg-desktop`. Use the more abstract `$screen-{xs,sm,md,lg,xl}-*` variables instead.
+* `@screen-sm`, `@screen-md`, `@screen-lg`. Use the more clearly named `$screen-{xs,sm,md,lg,xl}-min` variables instead.
+* `@screen-xs`, `@screen-xs-min`. The extra small breakpoint has no lower bound, so these variables were logically absurd. Reformulate your expression in terms of `$screen-xs-max` instead.
+* `@grid-float-breakpoint`
+
 ## Additional notes