yii2-bootstrap/docs/guide/helper-html.md

Html helper

Bootstrap introduces many consistent HTML constructions and skeletons, which allow creating different visual effects. Only the most complex of them are covered by the widgets provided with this extension. The rest should be composed manually using direct HTML composition. However, several special Bootstrap markup cases are covered by \yii\bootstrap\Html helper. \yii\bootstrap\Html is an enhanced version of the regular \yii\helpers\Html dedicated to the Bootstrap needs. It provides several useful methods:

• icon() - allows rendering of Glyphicon icons
• staticControl() - allows rendering of form "static controls"

\yii\bootstrap\Html inherits all functionality available at \yii\helpers\Html and can be used as a substitute, so you don't need them both inside your view files. For example:

<?php
use yii\bootstrap\Html;
?>
<?= Button::widget([
    'label' => Html::icon('approve') . Html::encode('Save & apply'),
    'encodeLabel' => false,
    'options' => ['class' => 'btn-primary'],
]); ?>

Attention: do not confuse \yii\bootstrap\Html and \yii\helpers\Html, be careful of which class you are using inside your views.