framework/helpers/BaseHtml.php
protected static function setActivePlaceholder($model, $attribute, &$options = [])
    {
        if (isset($options['placeholder']) && $options['placeholder'] === true) {
            $attribute = static::getAttributeName($attribute);
            $options['placeholder'] = $model->getAttributeLabel($attribute);
        }
    }
protected static function setActivePlaceholder($model, $attribute, &$options = [])
    {
        if (isset($options['placeholder']) && $options['placeholder'] === true) {
            $attribute = static::getAttributeName($attribute);
            $options['placeholder'] = $model->getAttributeLabel($attribute);
        }
    }
Generate placeholder from model attribute label.

@param Model $model the model object
@param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
about attribute expression.
@param array $options the tag options in terms of name-value pairs. These will be rendered as
the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
@since 2.0.14