framework/helpers/BaseHtml.php
public static function encode($content, $doubleEncode = true)
    {
        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
    }
public static function encode($content, $doubleEncode = true)
    {
        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
    }
Encodes special characters into HTML entities.
The [[\yii\base\Application::charset|application charset]] will be used for encoding.
@param string $content the content to be encoded
@param bool $doubleEncode whether to encode HTML entities in `$content`. If false,
HTML entities in `$content` will not be further encoded.
@return string the encoded content
@see decode()
@see https://secure.php.net/manual/en/function.htmlspecialchars.php