Liberalism at it's core is about inclusion and giving people wider latitude to be themselves free from discrimination or judgement. In a political sense, that may mean supporting a strong social safety net for the poor and those who may one day be poor, defending the human and civil rights of all people and especially minorities who's rights are more frequently violated, and so on and so forth.
In a theological sense it may involve supporting some or all of those political initiatives, but it also means being sticking up for the little guy (or gal) when it comes to religious matters, protecting human rights, and trying to include as many points of view as possible. My inclination would be to say that if you want a forum where everyone insists that homosexuality and abortion are the only two issues and that hating on homosexuals trumps people getting health care they need to survive or making sure the elderly and disabled get a monthly check so they can live lives of dignity and choice, then this may not be a place you'll enjoy. I don't think we're going to wind up having "litmus test" type issues, but at the same time the liberal in the name does lend the impression that we'll be leaning towards a certain mode of thought, though individual posters may not lean entirely that way and can still be liberal or progressive. I think the idea of the forum is to allow people to say what is in their hearts, particularly stuff from a liberal or progressive perspective.
In real life, progressives also sometimes favor things like married clergy, female clergy, homosexual clergy, gay marriage, and so on and so forth. The rules of the site limit what we can say about homosexuality, and not every progressive is going to support female clergy or married clergy or whatever. *However*, in this forum those views are protected and can be expressed without fear of anyone using harsh or abusive language against the person expressing those views.
Also, I think we'll be given more room here to say, for example, that we think as a result of the childhood abuse scandal, the way the church governs itself needs to be reformed and that there should be more participation in church governance by non-clergy. If some believe that maybe the scriptures are not inerrant in their entirety but rather sacred impressions about God, and that God did not tell people to wipe out entire cities including the women and children, or that the historical Jesus who walked the earth is a bit different from the accounts in the bible and in tradition, people will be able to express those points of view, even though they obviously will not be held by every liberal or progressive here.
Someone from the Jesus seminar might qualify as a progressive Catholic, for example, though that isn't the only definition of progressive (They are just one sub-group within a wider sub-group):
Jesus Seminar - Wikipedia, the free encyclopedia
People also would be allowed to think God in different ways, as feminine, or as someone who doesn't threaten sinners with hellfire. I think we'd be allowed to be universalists if we wanted to. Or not.
But I think mainly from a Catholic perspective, we're talking about things like opposing unjust wars, opposing the death penalty, supporting social justice for the poor, universal health care, stewardship of the environment, and so on and so forth. More Oscar Cardinal Romero than Joseph Cardinal Ratzinger, you know? More Pope Francis than Pope John-Paul II. More Jesuit than Opus Dei. Not necessarily unorthodox theology, just a different emphasis than some Catholic forums. Stuff that is all official Catholic teaching.
Hopefully, for example, here I'd be able to argue vigorously that evolution is scientific fact and the creationism is unscientific and laughable in this day and age if I want to. If I want to do a good natured parody where I pretend to believe the earth is flat, which seems not to be allowed elsewhere, hopefully that's okay too. Creationism shouldn't be protected on a liberal sub-forum. If anything, evolution should be protected. And, as you are probably aware, Pope Francis has said publicly that "God is not a wizard" and seemed to endorse evolution as a Catholic idea, and every Pope beginning with Pius XII if not before said evolution is an acceptable view for Catholics. A Catholic priest came up with the Big Bang theory.
Also, I would hope ultimately that we are allowed to do what liberals do, which is be accepting of people, and welcome in Anglicans, Lutherans, and other liturgical progressive Christians who consider themselves Catholic to be considered full Catholics and members for the purpose of this forum.
What is going to be interesting here is what the site allows and what it doesn't. I would like more freedom to be ourselves here than site rules allow, but I think the forum specific rules allow more freedom than most other forum specific rules by design, even if they are't the type of thing that would be done on a progressive site (In the sense that the site rules that set the table are in some cases not what a progressive would write- for example, a progressive forum from scratch would likely allow "promoting homosexuality", whatever that means).
Conservatism is often about shoving ones views down everyone's throat. Hopefully people will let us be who we are here, but I have a feeling people will complain about this forum because, you know, it allows people to say things they disagree with, even though they could easily just not visit a sub-forum labeled "liberal" if liberal stuff offends them.
Conservatives are welcome here to post fellowship stuff, but they aren't allowed to come here and debate or insult progressives and call us heterodox or whatever. This is a specifically liberal sub-forum and a safe haven.
Someone doesn't have to progressive on everything to be progressive, though, of course.