Php expression is not allowed as field default value

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In PHP, you cannot use a PHP expression as a default value for a field. The default value of a field should be a constant value that is known at the time the HTML page is loaded. PHP expressions are executed on the server-side before the HTML page is rendered, so they cannot be used as default field values.

However, you can use JavaScript to dynamically set the field value based on some condition or calculation. JavaScript is a client-side scripting language that runs in the browser and can manipulate the HTML page after it has been loaded.

Here’s an example of using JavaScript to set the default value of a field based on a condition: 

    
      <script>
        function setDefaultValue() {
          var field = document.getElementById("myField");
          var defaultValue = (someCondition) ? "default value 1" : "default value 2";
          field.value = defaultValue;
        }
        
        setDefaultValue();
      </script>
    
      <input type="text" id="myField" />

In this example, the JavaScript function setDefaultValue is called on page load. It retrieves the field element using document.getElementById and sets the default value based on the condition someCondition. If the condition is true, it sets the value to “default value 1”, otherwise it sets it to “default value 2”.

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