Interesting, I do have this option on a 4300:
ps@ex4300-test# set protocols rstp bpdu-destination-mac-address ?
Possible completions:
provider-bridge-group 802.1ad provider bridge group address
{master:0}[edit]But not on a 4200. This page:
states "In addition to the TPID EtherType value of 0x8100, EX Series switches that run Junos OS that does not support the Enhanced Layer 2 Software (ELS) configuration style also support values of 0x88a8 (Provider Bridging and Shortest Path Bridging) and 0x9100 (Q-inQ)."
So this suggests non-ELS switches such as the 4200 support provider bridging via ethertype as opposed to MAC address.