OK....The first thing you need to do is to seperate the group of FROMs, VIAs, and TOs that are ORed together.

You get to pick one FROM, VIA, and TO and link them together.

This will give you something like:

FROM ATL-UA-CHI-
VIA UA-CLE/DTT/DAY/CMH/IND/RDU-
TO UA-NYC/WAS-UA-JAX-UA-TPA-UA-MIA*

merged together this becomes:

ATL-UA-CHI-UA-CLE/DTT/DAY/CMH/IND/RDU-
UA-NYC/WAS-UA-JAX-UA-TPA-UA-MIA*

Next whereever there is a group of locations seperated by slashes you get to choose one.

So we would now have:

ATL-UA-CHI-UA-RDU-UA-NYC-UA-JAX-UA-TPA-UA-MIA*

Finally you are allowed to delete intermediate stops. Most likely you will have to as you are not allowed to revisit a city, many times the route will contain segments that aren't flown (e.g. SFO-OAK), and usually there is a limit to how many segments can be flown. So you might reduce our example to

ATL-UA-CHI-UA-RDU-UA-NYC-UA-MIA (or about 2840 miles instead of the 595 or so you would get with a direct flight).

So, a valid routing is anything that you can end up with after processing the routing rules as shown above.

One thing to note is that when getting the routing from expedia, the routing is often truncated due to lack of room. Often you can determine the complete routing by looking up the (also truncated) routing in the other direction and figuring out what the whole thing is based on the two pieces (assuming each piece is over 50% of the whole).

Hope this helps.