Content page customization in Drupal

If you want to customize Content page (admin/content/node) in Drupal (on screen below) you can insert form altering hook:

/**
 * Implementation of hook_form_alter().
 */
function custom_form_alter(&$form, $form_state, $form_id) { 
 if($form_id == 'node_admin_content') { // form overview name 
  // available fields:
  // $form['admin']['title'][nid]
  // $form['admin']['name'][nid]
  // $form['admin']['username'][nid]
  // $form['admin']['status'][nid]
  // $form['admin']['language'][nid]

  // or in simplest way
  echo "
";
  print_r($form['admin']);
  echo "
";
 }
}