[Freeswitch-dev] Help on switch_channel_expand_variables(switch_channel_t *channel, const char *in)

Hi, Could somebody shed some lights on how the mentioned method works ? What does it do exactly ? My best guess is it takes in a channel, a string and does something to the string (escape the string ? split the string ? or something like that? But why need a channel parameter?) If there is already an explanation somewhere about this, please point it out for me or possibly just tell me what configuration should I make to trigger this method to be called. I can use debugger and figure it out by myself. Any help would be greatly appreciated. Thanks very much Regards Alex To