How does a htb qdesc tree handle bandwidth overallocation?

let's say I have a simple htb hierarchy (See [man 8 tc-htb](https://linux.die.net/man/8/tc-htb)) set up where the total bandwidth specified for child htb classes *exceeds* the total bandwidth specified for the root htb class:

tc class add dev eth0 parent 1: classid 1:1 htb rate 100kbps
tc class add dev eth0 parent 1:1 classid 1:10 htb rate 70kbps
tc class add dev eth0 parent 1:1 classid 1:11 htb rate 70kbps
tc class add dev eth0 parent 1:1 classid 1:12 htb rate 70kbps

Here the maximum for the root htb class is 100kbps, but the collective maximum for child htb classes is 160kbps. How would the kernel handle all three children generating traffic at their maximum rates? Can I use an intermediary sfq to ensure fair treatment of aggregate traffic in this case? More importantly, how does the kernel decide which traffic to let through if the total traffic being generated exceeds the bandwidth of the hardware interface?