the "eXer" verbs--what does this mean?

Question

I find the use of the "X" here somewhat confusing. Is it standing in for "any consonant"? Or rather, any consonant except for "t" and "l"? If so, why does the first example show "compléter" as an example of a "eXer" verb? There seem to be two other ways of expressing this "any consonant" stand in on this site. I find "(-)" is used in some lessons, and "*" is used in others. None of the three are explained anywhere that I could find.

This seems needlessly confusing to me.

I just discovered this site and am very impressed otherwise.

Answer

It looks like those verbs are defined in this lesson: Conjugate -é(-)er, -e(-)er verbs - except -eter and -eler - in the present tense in French (Le Présent)

It looks like "X" in éXer/eXer represents one or multiple consonants ("célébrer" is given as an example), excluding -ETER and -ELER verbs.