Wix Form: RichTextBox - set required and set min & max value.lenght

I have some problems with a richTextBox.
When I set it as required ( let RichText = $w(“#richTextBox1”).required = true; ) it doesn’t get red outlined, if it isn’t valid.

“Link Website” has no value and is red outlined.
The richTextBox has no value and isn’t red outlined.

Do I need another code for this box ?

How can I set the richTextBox valid ? For all other text input fields this code works:

 if (!$w("#input42").valid) {
         // code line 

I need a code, that runs a function, if the value is between 900 and 2000.

I tried something like this

if ($w("#richTextBox1").value.lenght > 200) {
 //my code


if ($w("#richTextBox1").value.substr(900, 2000) {

but it isn’t working.