Function chain_op_names 

pub fn chain_op_names(
    cast: Option<i32>,
    steps: &[ChainStep],
) -> Vec<&'static str>

The operators a chain lowers to, in order: ["Mul", "Add"], ["Cast", "Mul", "Mul"].

One name per node the ONNX and TFLite backends emit, because that is what a vendor support matrix has to be asked about: a chain is several ordinary operators, not one fused operator that no matrix lists. Asking about the joined name reports Mul+Add as unsupported on hardware that supports both a multiply and an add.