I am not sure if they use any special legal construct, but last time I played around with Ada, the full Ada standard was available for free. The actual standard

I am not sure if they use any special legal construct, but last time I played around with Ada, the full Ada standard was available for free. The actual standard, not some revised draft. On top of that the rationale document which explains many of the design decisions was also available for free. (It's been a while, but I found these rationale documents fascinating reading.)