The can only be a single prefix. In this case, the comma character represents a pause, or delay of around 250msec. It does not mean punctuation seperator.

So for your example, the dial peer would match on the destination pattern of 7844. By default, a POTS dial peer will strip any explicitly matched digits - if the actual digit string was 7844, nothing would be sent out the voice port.

Which makes the next command 'forward-digits 0' irrelevant, since there will be no matched digits sent out the voice port!

The prefix command is used to prefix the digit string to any digits that would be sent out the voice port after matching on the destination pattern.

So in this case, the actual digit string that goes out the port would be 4429<250msec pause>4977<250msec pause>66

Sometimes a pause is needed to allow the recieving device to buffer digits, or play a new tone, or give it time to route the call before accepting IVR or DID digits.

Maybe a better example would be this -

dial-peer voice 1234 pots

destination-pattern 8446....

port 0/0/0

prefix 011,,,,6128446

In this case , if the called number 84467800 matches on dial peer 1234, we would match on all digits, send them out port 0/0/0 , but first we would dial 011, wait 1 second, then dial 612 and re-add the 8446 plus the 7800 string that matched via the '.' regular expression.