MinLength

Checks if the number of characters in the value equals or is greater than the given minimum

This validator works like Min but it always checks for string length, even if a numeric value is given. The min validator will check for the value of the number in that case.

In your code

if(v::minLength('Lorem ipsum dolor sit amet.', 10)) {
  echo 'Yay, valid!';
}

In panel fields

fields:
  example:
    label: Example field
    type: text
    validate:
      minLength: 10