Drupal 7 Module Development: Config form

espn_news.module

<?php

  /**
   * Implements hook_form().
   *
   * Creates a configuration form. See the API reference for info on different
   * form inputs.
   *
   * From API Reference: https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7
   *
   * @url: https://api.drupal.org/api/drupal/modules!node!node.api.php/function/hook_form/7
   */
  function espn_news_form($form, &$form_state) {
    // Fieldset.
    $form['espn_api'] = array(
      '#type' => 'fieldset',
      '#title' => t('ESPN API'),
      '#weight' => 0,
      '#collapsible' => TRUE,
      '#collapsed' => FALSE,
    );
    // Textfield for API key.
    $form['espn_api']['espn_news_api_key'] = array(
      '#type' => 'textfield',
      '#title' => t('ESPN API key'),
      '#default_value' => variable_get('espn_news_api_key'),
      '#size' => 40,
      '#maxlength' => 24,
      '#description' => t('API from ESPN Developer Center (http://developer.espn.com/apps/mykeys).'),
      '#required' => TRUE,
    );

    return system_settings_form($form);
  }