Number form field type
From Joomla! Documentation
The number form field type provides a HTML5 text box with arrows. If the field has a value saved, this value is displayed when the page is first loaded. If not, the default value (if any) is used. Available from 
- type (mandatory) must be number.
- name (mandatory) is the unique name of the field.
- label (optional) (translatable) is the descriptive title of the field.
- description (optional) (translatable) is text that will be shown as a tooltip when the user moves the mouse over the drop-down box.
- default (optional) (translatable) is the default value.
- class (optional) is a CSS class name for the HTML form field.
- min (optional) this value is the lowest that can be chosen.
- max (optional) this value is the highest that can be chosen.
- step (optional) if user click up/down arrow current value will change by this attribute (this attribute value will be added or subtracted to current field value).
- filter (optional) the filter to be used on this field value after submit.
- hint (optional) placeholder to be set on this field.
- disabled (optional) should this field be disabled?
- readonly (optional) should this field be read only?
- required (optional) should this field be required?
- autocomplete (optional) should this field use auto complete?
- autofocus (optional) should this field have focus when page first time loads?
- size (optional) the maximum field width in characters.
Example XML field definition which would create a number box with possibility to chose values between 0 and 10 and change current value by 1 each time user click up/down field button.
<field name="mynumbervalue" type="number" default="0" label="Choose an number" description="" min="0" max="10" step="1" />