org-link-types-re

org-link-types-re 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:
Matches a link that has a url-like prefix like "http:"