See, for instance, the Thirteenth and Fifteenth sessions of Trent. Here’s a selection from the decrees of the Fifteenth; the bold is mine, and in case it is too long (but who can’t make time in his day to read the decrees of the Sacred Council of Trent?) I will sum it up at the end:
DECREE FOR PROROGUING THE SESSION
Whereas, in pursuance of the decrees made in the last Sessions, this holy and universal Synod has, during these days, most accurately and diligently treated of the things which relate to the most holy sacrifice of the mass, and to the sacrament of order, with the view that, in the Session held on this day, It might publish, as the Holy Ghost should have suggested, decrees on these subjects, and on the four articles concerning the most holy sacrament of the Eucharist, which had been finally deferred to this Session ; and whereas it was thought that, in the interim, there would have presented themselves at this sacred and holy Council those who call themselves Protestants, for whose sake It had deferred the publication of the said articles, and to whom It had given the public faith, or a safe-conduct, that they might come freely and without any hesitation; nevertheless, seeing that they have not as yet come, and the holy Synod has been petitioned in their name, that the publication which was to have been made on this day, be deferred to the following Session, an assured hope being held out that they will certainly be present long before that Session, upon receiving in the meanwhile a safe-conduct in a more ample form : . . .
SAFE-CONDUCT GIVEN TO THE PROTESTANTS
The sacred and holy, ocecumenical and general Synod of Trent,-lawfully assembled in the Holy Ghost, the same Legate and Nuncios of the Apostolic See presiding therein,–adhering to the safe-conduct given in the last Session but one, and enlarging it in the manner following,–certifies to all men,- that by the ten our of these presents, It grants and wholly concedes the public faith, and the fullest and most true security, which they entitle a safe-conduct, to all and singular the priests, electors,-princes, dukes, marquises, counts, barons, nobles, soldiers, commonalty, and to all other persons whatsoever, of what state, condition, or quality soever they may be, of the province and nation of Germany,- and to the cities and other places thereof, and to all other ecclesiastical and Secular persons,- especially those of the Confession of Augsburg,- who shall come, or shall be sent with them, to this General Council of Trent, and to those that shall set forth, or have already repaired hither,- by whatsoever name they are entitled, or may be designated,–to come freely to this city of Trent, and there to remain, abide, sojourn, and to propose, speak and treat of, examine and discuss, any matters whatsoever together with the said Synod, and freely to present and set forth all whatsoever they may think fit, and any articles what-ever, either in writing, or by word of mouth, and to explain, establish, and prove them by the sacred Scriptures, and by the words, passages, and reasons of the blessed Fathers, and to answer even, if it be needful, to the objections of the General Council; and to dispute, or to confer in charity, without any hindrance, with those who may have been selected by the Council, all opprobrious, railing, and contumelious language being utterly discarded; and in particular, that the controverted matters shall be treated of in the aforesaid Council of Trent, according to sacred Scripture, and the traditions of the apostles, approved Councils, the consent of the Catholic Church, and the authorities of the holy Fathers; with this further addition, that they shall not be punished under pretence of religion,- or of offences already committed, or that may be committed, in regard thereof; as also, that the divine offices shall not, on account of their presence, be in any way interrupted, either upon the road, or in any place during their progress, their stay, or their return, or in the city of Trent itself; and that, upon these matters being concluded, or before they are concluded,- if they, or any of them, shall wish, and whensoever such is their or his pleasure, or the command and leave of their superiors, to return to their own homes, they shall forthwith be able at their good pleasure,- to return freely and securely . . . .
. . . It also reciprocally wills, that if, which God forbid, any one, or divers, of this Synod, should, either on the road, or whilst sojourning at, or returning therefrom, perpetrate or commit any heinous act, whereby the benefit of this public faith and assurance may be violated, or in any way set aside, the persons discovered in any such crime shall be forthwith punished by the Synod itself, and not by others,- with a proportionate chastisement and a sufficient reparation, which the Germans of the Confession of Augsburg, who may be present here at the time, may on their part justly approve of and commend,-the present form, conditions and terms of the safe-conduct remaining wholly untouched thereby. . . .
That’s right, they prorogued a whole session of Trent and delayed the publication of articles about the Mass and the Eucharist to give Protestant extra time to come and propose their ideas “and to explain, establish, and prove them by the sacred Scriptures.”
) to please the Protestants, to become more Protestant, and so on and so forth. Yet obviously we do not think that in the case of the Council of Trent. This goes to show that arguments about what is “Protestant” have to be made on the basis of the facts, not of insinuations deriving from who was invited to what council.
I’ve limited the information provided here so I don’t get myself in trouble.