I opened up SciSnap! and saw that CALL had a read only input, (which CALL doesn’t have, so it must be bootstrapped. I opened a new Snap! tab and opened SciSnap! to verify this, and yes, CALL is bootstrapped (but has no new definition.)
What do you mean by “bootstrapped”?
the call block turned into the custom block (i.e. the inputs are now read-only) if you load scisnap.
Means the block was marked as ' Primitive written in Snap! ' even though it doesn’t need to be (+, it’s still quite a buggy feature.)