org-bracket-link-analytic-regexp

org-bracket-link-analytic-regexp is a variable defined in `org.el'.
Its value is

"\\[\\[\\(\\(doi\\|elisp\\|f\\(?:ile\\(?:\\+\\(?:\\(?:emac\\|sy\\)s\\)\\)?\\|tp\\)\\|https?\\|m\\(?:ailto\\|essage\\)\\|news\\|shell\\):\\)?\\([^]]+\\)\\]\\(\\[\\([^]]+\\)\\]\\)?\\]"

Documentation:
Regular expression used to analyze links.
Here is what the match groups contain after a match:
1: http:
2: http
3: path
4: [desc]
5: desc