[supriyo-biswas]

Browsers do have this, although this measure is only selectively applied for certain CAs where misissuance has been an issue (There was a Indian CA for which this was used, need to look around MDSP for the link. I’ll post it shortly.)

[agwa]

Historically, root constraints were only used in response to misissuance, but more recently, KamuSM voluntarily limited themselves to .tr when they applied.