validations

Assuming the field you're using to capture the data is an Integer field you can write a validation on that field:

{
  a!integerField(
    label: "Integer",
    labelPosition: "ABOVE",
    value: ri!myInteger,
    saveInto: {
      ri!myInteger
    },
    refreshAfter: "UNFOCUS",
    validations: {
      if(
        fn!or(
          ri!myInteger<0,
          ri!myInteger>99
        ),
        "Invalid value - out of range (0-99)",
        null
      )
    }
  )
}

I use a text field and user can enter a value a list from 01-99. Is it possible to use regexallmatches for this to validate and get the correct  values 

As long as you can find the correct RegEx expression then yes. I would encapsulate the RegEx in a separate Expression Rule so you can test it independently from the User Interface, and then simply incorporate it into the Interface when it's ready.

As long as you can find the correct RegEx expression then yes. I would encapsulate the RegEx in a separate Expression Rule so you can test it independently from the User Interface, and then simply incorporate it into the Interface when it's ready.