Some AccessFlag parsing methods throw IAE because a flag mask is not valid in a location. However, there is no easy way to check what flag mask bits or what flags are valid for a location. We need such APIs to check, specific to each class file format version.

API would look like:
int flagsMask(CFFV); int flagsMask();
Set<AF> flags(CFFV); Set<AF> flags();

Also in the investigation, it's noted that ACC_SYNTHETIC is incorrectly represented - it is available since release 5.0 instead of release 7. This bug is fixed together for implementation simplicity.