Range slider

If you want to allow users to specify a value which is in a specific range, you can consider use of the range slider field.

Thanks to the use of the min, max and step parameters you can easily limit available values:

{
    "name": "fontSize",
    "label": "Font size",
    "group": "Fonts",
    "note": "The font-size of the root element in REM unit",
    "value": "1.1",
    "type": "range",
    "min": 1,
    "max": 3,
    "step": 0.05 
}

Above code will create a range slider which allows users to select a value between 1 and 3 with minimal step equal to 0.05.