+ * The regular expresion contains 6 different sub matches to help with parsing.
+ *
+ * 1/6 - An extra [ or ] to allow for escaping shortcodes with double [[]]
+ * 2 - The shortcode name
+ * 3 - The shortcode argument list
+ * 4 - The self closing /
+ * 5 - The content of a shortcode when it wraps some content.
+ *