Should follow Coder's best practices.

I did a code review using Coder recently on the aggregator module. It's a useful reference I think and hope that we can standardize core

modules/aggregator/aggregator.module

#
Line 30: String concatenation should be formatted with a space separating the operators (dot .) and the surrounding terms

      $output .= '<dd>' .  t('A <a href="@aggregator-opml">machine-readable OPML file</a> of all feeds is available. OPML is an XML-based file format used to share outline-structured information such as a list of RSS feeds. Feeds can also be <a href="@import-opml">imported via an OPML file</a>.', array('@aggregator-opml' => url('aggregator/opml'), '@import-opml' => url('admin/config/services/aggregator'))) . '</dd>';

#
severity: normalLine 32: String concatenation should be formatted with a space separating the operators (dot .) and the surrounding terms

      $output .= '<dd>' .  t('A correctly configured <a href="@cron">cron maintenance task</a> is required to update feeds automatically.', array('@cron' => 'http://drupal.org/cron')) . '</dd>';

#
severity: normalLine 310: Use ANSI standard <> instead of !=

  $result = db_query('SELECT * FROM {aggregator_feed} WHERE queued = 0 AND checked + refresh < :time AND refresh != :never', array(

modules/aggregator/aggregator.processor.inc
aggregator.processor.inc

    *
      severity: criticalLine 82: Potential problem: FAPI elements '#title' and '#description' only accept filtered text, be sure to use c(), f() or similar to ensure your $variable is fully sanitized.

              '#description' => $info['description'],