I have a requirement where in a text field needs to be formatted in a specified format of "X.1234567"

Try this - it doesn't even allow the user to enter anything that would throw a validation error (as far as i can tell), as it automatically reformats any number or text entered into the desired result.  It also (by brute force) caps the length of the number following "X." to 7 total digits.  You may need to adjust slightly, depending on the particular behavior you want.

a!textField(
  value: local!text,
  saveInto: {
    a!save(
      local!text,
      left(
        "X." & text(
          todecimal(cleanwith(save!value, "0123456789")),
          "0000000"
        ),
        9
      )
    )
  }
)