JACKSONVILLE – It's Dress Rehearsal Friday, but it's so much more.

Yes, the Jaguars want to use the third game of the 2015 preseason as every NFL team uses the third game of every preseason – as the closest-thing-to-the-real-thing preseason game and therefore, as the best tune up for the regular season.

But Lions-Jaguars Friday at 8 p.m. at EverBank Field is more than that for the Jaguars.

That's because while the 2015 Jaguars have looked really good in some really important areas in the first two preseason games, they're still very much a team in the developing stages.

There are also things the Jaguars haven't yet seen that they must see, and those are areas to watch Friday. Highlighting that area: T.J. Yeldon and Chris Clemons. To different degrees, the career and seasonal debuts of those players are compelling areas to watch Friday.

So, what to watch on Dress Rehearsal Friday?

Here are five storylines, which include three "debuts," an area of improvement and the one thing the Jaguars simply have to keep seeing:

1)The debut of T.J. Yeldon.This is the game's biggest story from the Jaguars' perspective. As good as the offense has looked in preseason – and compared to the past several seasons, it has looked very good – it has looked that way without Yeldon. That makes what's going on doubly intriguing because while the running game has been productive, Yeldon is the type of back who can turn productivity into game-changing pop. A finger injury kept him out of the first two preseason games. He probably could have played Saturday against the Giants, and he could work with the starting unit extensively Friday. Maybe he starts the season and maybe doesn't, but there's little doubt he will be key to the offense. He has shown a knack in practice for making defenders miss, and for making tough runs look easy. If he can show that in games, this running game's going to be intriguing.

2)The debut of the Wisniewski-led O-line.The new element here is Stefen Wisniewski, named the starting center this week. That will make this the most extensive look of the preseason for the first-team line, but mostly the Jaguars just want to see this group do what it has been doing: keep Blake Bortles clean and keep creating opportunities in the run offense. The Lions may be the best defensive line the Jaguars have faced. If the offensive line fares well Friday, that's its best preseason sign yet.

3)Chris Clemons/pass rush.The veteran made news in the offseason by not participating in voluntary workouts. He made news again by spending the first part of training camp on the active non-football injury list. All of those news stories become less significant if Clemons produces during the regular season. And make no mistake: the Jaguars need him to produce. The pass rush has been silent in two preseason games. That doesn't mean it will be silent in mid-September, but this area must produce.

4)Hold on to it.The wide receivers group has become an area to watch. We won't say "area of concern," because there's much to like, but the loss of Arrelious Benn this week didn't help. There's also the status of Marqise Lee's hamstring. Will someone emerge as a potential third/fourth/fifth receiver? Rookie Rashad Greene has shown flashes; veteran Bryan Walters has been consistent through two preseason games, so he's a candidate. One key area: drops. This isn't just the receivers, but it has been an issue in two preseason games.  There's potential in the receiver group, but it's still developing. Drops are going to happen, but the Jaguars had six last week. Too many.

5)Blake Bortles.This is the gotta-keep-seeing area. The Jaguars' second-year quarterback has been good so far this preseason. Really good. He has done what you wanted to see. He looks better. He looks more confident. Perhaps the best news for the Jaguars is he has done nothing spectacular. That gives you the idea that he can keep doing the things he's doing. That's what the Jaguars want to see from Bortles Friday. Let him play one more half, see some good solid things you trust and get him out. As far as preseason is concerned, that's mission accomplished.