src/Form/Element/FileUpload.php
public function setIsMultiple($flag)
    {
        $this->isMultiple = (bool) $flag;
        if ($flag) {
            $this->setAttribute('multiple', true);
        } else {
            $this->removeAttribute('multiple');
        }

        return $this;
    }
public function setIsMultiple($flag)
    {
        $this->isMultiple = (bool) $flag;
        if ($flag) {
            $this->setAttribute('multiple', true);
        } else {
            $this->removeAttribute('multiple');
        }

        return $this;
    }
Sets if this element allows multiple files to be selected.

@param boolean $flag

@return self