Add specific validation to text

You can use regex functions to match with specific text pattern and use its result for displaying validation on the text field. 

{
  a!textField(
    label: "Release Version",
    labelPosition: "ABOVE",
    value: ri!value,
    saveInto: {
      ri!value      
    },
    refreshAfter: "UNFOCUS",
    validations: {
      if(
        regexmatch(
          "^(\d+\.)(\d+\.)(\*|\d+)$",
          ri!value
        ),
        {},
        "Enter correct format XX.XX.XX"
      )
    }    
  )
}

Use this web based tool to explain / understand the regex pattern - https://regexr.com/