There are quite a few cards with multiple parts:
- split (including fuse)
- flip
- dfc
- meld
Currently json data doesn't indicate which part is "primary" (directly playable) and which isn't. I thought about coming up with some rules downstream, but they're fairly silly:
- split - all are primary
- dfc - the one with mana cost generally primary, except Westvale Abbey is special case
- flip - both have same mana cost as per
rule 709.1c, so the only way is grepping A vs B in card number
- meld - same as for DFCs, except for Hanweir Battlements as special case
Terminology "part type", "primary", "secondary" has no rules meaning, I just came up with that to describe the problem, feel free to use completely different wording.