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vendor/yiisoft/yii2-bootstrap5/docs/guide/migrating-yii2-bootstrap.md

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+Migrating from yii2-bootstrap4
+==============================
+
+yii2-bootstrap5 is a major rewrite of the entire project (according Bootstrap 5 to Bootstrap 4 migration guide).
+The most notable changes are summarized below:
+
+## General
+
+* The namespace is `yii\bootstrap5` instead of `yii\bootstrap4`
+* The php compatibility **is limited to** `>=7.0`
+* The close buttons of widgets like [[yii\bootstrap5\Alert|Alert]] or [[yii\bootstrap5|Modal|Modal]] now gets rendered
+  via CSS and does not have any content anymore. So be sure to remove `btn-close` class and set appropriate styles yourself
+  if you override it.
+
+## Widgets / Classes
+
+### BaseHtml
+
+### ActiveField
+
+### ActiveForm
+
+There is a new constant [[yii\bootstrap5\ActiveForm::LAYOUT_FLOATING]]. It's a 
+[new form layout](https://getbootstrap.com/docs/5.1/forms/floating-labels/) introduced in Bootstrap 5.
+
+### Breadcrumbs
+
+### ButtonDropdown
+
+### ButtonToolbar
+
+### Carousel
+
+### LinkPager
+
+### Modal
+
+Change `data-target` and `data-toggle` to `data-bs-target` and `data-bs-toggle`
+
+### Nav
+
+### NavBar
+
+There is now the possibility to create an [offcanvas navbar](https://getbootstrap.com/docs/5.1/components/navbar/#offcanvas).
+You can achieve this by setting the `$collapseOptions` to `false` in [[yii\bootstrap5\NavBar|Navbar]] widget and the 
+`$offcanvasOptions` to at least an empty array.
+
+### Tabs
+
+### ToggleButtonGroup