Oh I am in version 11 with this environment and I don't see this. Maybe it is a feature of 12?

What version are you in?

Darn! I'm on Cloud, but this isn't a new feature as far as I can remember.

Do you have the option in number fields by any chance?

Yea I see it in Cloud. I also checked Version 12 On-Prem and I don't see it. I can do it for any other non currency number on the general tab and it looks like the screenshot below. Only currency does not allow me to set a range in the editor. The option exists because we can access it with JS, but it is not shown and the JS is not reliable.

For example we want to prevent submitting a form with a total as a negative value but the total field is populated as a total of other fields so the field itself is read only.

Check the Advanced tab on the Currency field.  This is from the latest Forms 11 

You could also set up a field rule to hide the submit button when the total field is less than 0, if that's an option for you?

Weird you're not seeing range limiting under Advanced though.

Seems the range on currency fields is only in the modern designer, all these forms are in Classic.

If I hide the submit button I also need to show a message near the field, which would work but not as clean as just limiting the range to above 0.

I guess there are custom solutions, but not sure why the min attribute is breaking on me on read only fields.

Hi @████████, try this JS code. It is for Classic Form. Let me know if help. 

$(document).on('ready.lfForm refresh-view.lfForm', function () {
  $('#Field75')                       // change to your selector
    .attr({
      'data-parsley-pattern' : '^\\$?(0|[1-9]\\d*)(\\.\\d{1,2})?$',
      'data-parsley-pattern-message' : 'Amount must be zero or positive'
    });
});

Tried this alternative attribute today without any luck either. I narrowed down the working vs non-working scenarios and found that forms which use the .val().change() method to set the total from JS do not work, while forms that use calculations to set the total do work.

As a workaround I am setting the maximum value on the input fields that the user enters in a way so that they can not create a negative total. This way they can still write JS to total when needed. Some forms use calculations for simpler calculations and some us JS for more complex calculations.

So when applying min and/or max attributes for a field it always works if the user has direct access to the field, but not when using .change() in JS to set a total.

readonly or not does not matter.

Try this other way: 

Create a Custom HTML object near your field. with this code inside: 

<!-- Error container for the currency field -->
<span id="err1" class="currency-error" style="display:none;"></span>

You can customize the id="err1" by any number you want. I prefer to put the same number as the input field. I need the alert, that way I never lose track. 

Keep the ID you put there, because you need to put the same in the JS code I will share next. 

$(document).ready(function () {

  const $currency = $('#Field1');           // <- update ID if needed.
  const $error    = $('#err1');

  // ------------- core validation -------------
  function validateCurrency() {
    let val = parseFloat($currency.val());

    // Treat empty or non-numeric as zero
    if (isNaN(val)) { val = 0; }

    if (val < 0) {
      // Show visual error
      $currency.addClass('invalid-negative');
      $error.text('Amount cannot be negative.').show();
      return false;                          // invalid
    } else {
      // Clear error state
      $currency.removeClass('invalid-negative');
      $error.hide();
      return true;                           // valid
    }
  }

  // ------------- event hooks -------------
  // 1) Manual typing
  $(document).on('input change', '#Field75', validateCurrency);

  // 2) Scripted changes (.val(), calculations, etc.)
  //    Laserfiche can rebuild the input; validate every 300 ms as backup.
  setInterval(validateCurrency, 300);

  // 3) Final safety net on submit
  $('form').on('submit', function (e) {
    if (!validateCurrency()) {
      e.preventDefault();                    // block submit
      alert('Currency value cannot be negative. Please correct it.');
    }
  });

});

Then using this CSS:

/* Red border when the value is invalid */
.invalid-negative {
  border-color: #d9534f !important;
}

/* Style for the inline error message */
.currency-error {
  color: #d9534f;
  font-size: 0.85rem;
  margin-left: 6px;
}

I tried it and it works for me. Let me know. 

-----

(Optional)

Another approach to prevent users type "-" in the input field. Replace my #Field1 by your input Field field id: 

$(document).on('keydown', '#Field1', function (e) {
  if (e.key === '-' || e.keyCode === 189) {
    e.preventDefault();           // prevents the “-” sign from being typed from the keyboard
  }
});