docs: public synchronized TextBox setValidationPattern(Pattern validationPattern) {
          if(validationPattern != null) {
              for(String line: lines) {
                  if(!validated(line)) {
                      throw new IllegalStateException("TextBox validation pattern " + validationPattern + " does not match existing content");
                  }
              }
          }
          this.validationPattern = validationPattern;
          return this;
      }