There are several versions of it, and the terminology keeps changing (i.e. they keep changing the definitions of familiar theological terms), so a lot depends on who you ask! But there are a few common threads:

One of the major things is that salvation is not so much a matter of individual justification, nor that justification is a "forensic declaration" of the individual's righteous standing before God, as it is a person's membership in the covenant. Signified by baptism, the individual must then "live up to their baptism" in order to attain salvation. But all baptized persons are counted as members of the covenant and inheritors of salvation.

It seems to me that there are, among those of us that tend to favor "paedocommunion" (letting kids take part in the Lord's Supper), some who are willing to turn the Reformation on it's head in order to justify paedocommunion. I think that is part of the reason FV got such a firm grip in the PCA before it was finally addressed.

Salvation-by-sacrament in a way, FV is virtually a call to return to Rome.