src/Drupal/Core/Template/AttributeValueBase.php
public function render() {
    $value = (string) $this;
    if (isset($this->value) && static::RENDER_EMPTY_ATTRIBUTE || !empty($value)) {
      return Html::escape($this->name) . '="' . $value . '"';
    }
  }
public function render() {
    $value = (string) $this;
    if (isset($this->value) && static::RENDER_EMPTY_ATTRIBUTE || !empty($value)) {
      return Html::escape($this->name) . '="' . $value . '"';
    }
  }
public function render ( ) { $ value = ( string ) $ this ; if ( isset ( $ this -> value ) && static :: RENDER_EMPTY_ATTRIBUTE || ! empty ( $ value ) ) { return Html :: escape ( $ this -> name ) . '="' . $ value . '"' ; } }
Returns a string representation of the attribute.

While __toString only returns the value in a string form, render()
contains the name of the attribute as well.

@return string
The string representation of the attribute.
Returns a string representation of the attribute .