framework/helpers/BaseHtml.php
public static function getInputId($model, $attribute)
    {
        $charset = Yii::$app ? Yii::$app->charset : 'UTF-8';
        $name = mb_strtolower(static::getInputName($model, $attribute), $charset);
        return str_replace(['[]', '][', '[', ']', ' ', '.'], ['', '-', '-', '', '-', '-'], $name);
    }
public static function getInputId($model, $attribute)
    {
        $charset = Yii::$app ? Yii::$app->charset : 'UTF-8';
        $name = mb_strtolower(static::getInputName($model, $attribute), $charset);
        return str_replace(['[]', '][', '[', ']', ' ', '.'], ['', '-', '-', '', '-', '-'], $name);
    }
Generates an appropriate input ID for the specified attribute name or expression.

This method converts the result [[getInputName()]] into a valid input ID.
For example, if [[getInputName()]] returns `Post[content]`, this method will return `post-content`.
@param Model $model the model object
@param string $attribute the attribute name or expression. See [[getAttributeName()]] for explanation of attribute expression.
@return string the generated input ID
@throws InvalidArgumentException if the attribute name contains non-word characters.