kamailio-kemi-framework: details about relation between cfg function and KEMI exports

kamailio-kemi-framework/docs/modules/header.md

@@ -1,3 +1,28 @@
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 # KEMI Module Functions #
-The following sections lists all exported KEMI functions. More information regarding the function can be found by clicking the KEMI prototype which will take you the original module's documentation.
+
+The following sections lists all exported KEMI functions. More information regarding
+the function can be found by clicking the KEMI prototype which will take you
+the original module's documentation.
+
+Because the native `kamailio.cfg` scripting language allows variadic functions,
+but exports to KEMI are functions with fixed number of parameters, there can
+be a group of KEMI functions to offer the capabilities of a single `kamailio.cfg`
+function. In such case, the KEMI functions share a common naming prefix, usually
+the name of the `kamailio.cfg` function.
+
+For example, the `kamailio.cfg` function `ds_is_from_list(...)` from `dispatcher`
+module has the prototype:
+
+```c
+int ds_is_from_list([groupid [, mode [, uri] ] ])
+```
+
+And the corresponding KEMI exports are:
+
+```c
+int KSR.dispatcher.ds_is_from_lists();
+int KSR.dispatcher.ds_is_from_list(int groupid);
+int KSR.dispatcher.ds_is_from_list_mode(int groupid, int mode);
+int KSR.dispatcher.ds_is_from_list_uri(int groupid, int mode, str "uri");
+```