--- /dev/null
+Extensions are routed according to priority, and may be based on any set
+of digits, #, and *. For each extension, several actions may be listed
+and each given a priority. When each action completes, it generally moves
+to the next priority (except for some modules which use explicity GOTO's.
+Extensions frequently have data they pass to the executing application
+(most frequently a string). There are some reserved application names:
+
+ GoTo: Go to a specific extension
+ Answer: Answer the line, if it hasn't already been answered
+
+Also, there are some extensions with important meanings:
+
+ s: What to do when an extension context is entered (unless
+ overridden by the low level channel interface)
+ i: What to do if an invalid extension is entered
+ t: What to do if nothing is entered in the requisite amount
+ of time.
+
+And finally, the extension context "default" is used when either a) an
+extension context is deleted while an extension is in use, or b) a specific
+starting extension handler has not been defined (unless overrridden by the
+low level channel interface).