无法在Joomla / PHP中添加自定义XML属性

'<field name="id_'.$filter_record['id'].'_hourfrom" type="integer"
                        label="from" description="Delivery Hour Range"
                         size="'.$filter_record['holdout'].'"
                        maxlength="20"
                        required="true"
                        class = "hourfrom"
                        first = "1"
                        last = "'.$filter_record['list_limit'].'"
                        step = "1"
                        filter="user_utc" />

i have this code above which dynamically generates input fields in the view using XML. The problem is I want to add a custom attribute so I can use it in javascript processing.

for example: value_type = "single"

When i try to add this in the code above, in the processed page, it is not displayed, i cannot also get the attribute.

Is there a proper way to do this?