The page gives your definition. I am look for the Church's definition of a public manifest formal heretic.
DEFINITION OF HERESYCan. 1325 (1917 Code) 1. The faithful of Christ are bound to profess their faith whenever their silence, evasiveness, or manner of acting encompasses an implied denial of the faith, contempt for religion, injury to God, or scandal for a neighbor. 2.
After the reception of baptism, if anyone, retaining the name Christian, pertinaciously denies or doubts something to be believed from the truth of divine and Catholic faith, [such a one is] a heretic; if he completely turns away from the Christian faith, [such a one is] an apostate; if finally he refuses to be under the Supreme Pontiff or refuses communion with the members of the Church subject to him, he is a schismatic.
Can. 751 (1983 Code)
Heresy is the obstinate denial or obstinate doubt after the reception of baptism of some truth which is to be believed by divine and Catholic faith; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Supreme Pontiff [i.e., the legitimate one] or of communion with the members of the Church subject to him.
IPSO FACTO LOSS OF ECCLESIASTICAL OFFICE FOR HERESYCanon 188 §4 (1917 Code): “Any office
becomes vacant upon the fact and without any declaration by tacit resignation
recognized by the law itself if the cleric…
Publicly defects from the Catholic faith.”
Canon 2314 §1 º2 (1917 Code): states that heretics, “unless they respect warnings they are deprived of…office…with the warning being repeated, are deposed.”
Canon 194 §1 º2 (1983 Code): “The following are removed from an ecclesiastical office
by the law itself…a person who has publicly defected from the Catholic faith or from the communion of the Church.” §2: “The removal mentioned in n. 2 can be enforced only if it is established by the declaration of a competent authority.”
So both 1917 and 1983 Canon Law provide that a public heretic loses his office automatically, but the physical “enforcement” of that vacancy (kicking the bum out) requires a “warning” or a “declaration” by Church authorities. There seems to be no real difference between 1917 and 1983 in this matter.