If the node is blacklisted from being mutated. This is for example when the node covers a C macro.
If the node should not be part of mutant schemata because it is highly likely to introduce compilation errors. It is for example likely when operators are overloaded.
Block nodes that have a high probability of failing from being coverage instrumented.
A block of code such such as a local scope enclosed by brackets, {}.
It is intended to be possible to delete it. But it may need to be further analyzed for e.g. Return nodes.