Pleased to oblige
![Nerd face :nerd: 🤓](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f913.png)
the Council of Trent, for one, sought the ‘expert’ participation of heretic Protestant leaders as well as Catholics. I quote from the Catholic Encyclopedia in regards to the background and leadup to Trent (with whole paragraph provided so no quoting out of context). Source
here
"On 2 June, Paul III published the Bull calling all patriarchs, archbishops, bishops, and abbots to assemble at Mantua on 23 May, 1537, for a general council. Cardinal legates were sent with an invitation to the council to the emperor, the King of the Romans, the King of France, while a number of other nuncios carried the invitation to the other Christian countries. The Netherlander Peter van der Vorst was sent to Germany to persuade the German ruling princes to take part.
The Protestant rulers received the ambassador most ungraciously; at Smalkald they refused the invitation curtly, although in 1530 they had demanded a council. "