Deconstruction of a URL-matching regular expression.

src/Linkification/Linkify.coffee

@@ -4,7 +4,33 @@ Linkify =
 
     # gruber revised + magnet support
     # http://df4.us/fv9
-    @catchAll = /\b([a-z][\w-]+:(\/{1,3}|[a-z0-9%]|\?(dn|x[lts]|as|kt|mt|tr)=)|www\d{0,3}\.|[a-z0-9.\-]+\.[a-z]{2,4}\/)([^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’])/g
+    @catchAll = ///
+      \b
+      (
+        [a-z][\w-]+:                 # URL protocol and colon
+        (
+          /{1,3}                     # 1-3 slashes
+          |                          #   or
+          [a-z0-9%]                  # Single letter or digit or '%'
+          |                          #   or
+          \?(dn|x[lts]|as|kt|mt|tr)= # Magnet parameters
+        )
+        |                          #   or
+        www\d{0,3}[.]              # "www.", "www1.", "www2." … "www999."
+        |                          #   or
+        [a-z0-9.\-]+[.][a-z]{2,4}/ # looks like domain name followed by a slash
+      )
+      (                                    # One or more:
+        [^\s()<>]+                         # Run of non-space, non-()<>
+        |                                  #   or
+        \(([^\s()<>]+|(\([^\s()<>]+\)))*\) # balanced parens, up to 2 levels
+      )+
+      (                                    # End with:
+        \(([^\s()<>]+|(\([^\s()<>]+\)))*\) # balanced parens, up to 2 levels
+        |                                  #   or
+        [^\s`!()\[\]{};:'".,<>?«»“”‘’]     # not a space or one of these punct chars
+      )
+    ///g
 
     Post::callbacks.push
       name: 'Linkify'