functional-equations has the same problem as functional-analysis, namely, it's a term that has a conventional meaning in advanced mathematics, a meaning that most casual users of this website will not know about. In particular, it's not a good tag for any old question that has an equation with a function in it. — Gerry Myerson yesterday

@GerryMyerson If needed, mention of alternative tags can be added to the functional-equation tag-excerpt. We have a comment template for functional analysis, similar template can be created for functional equations. And we can make suggestions of tag warnings in this thread. — Martin Sleziak yesterday

@GerryMyerson I have added similar sentence to the functional-equations tag-excerpt. If you see possible further improvements, please do edit it. (Of course, this only helps if the users adding tag actually look at the excerpt.) I did nothing about comment templates and tag warnings for (functional-equations). If you think that template or warning (or both) might be useful, either you or me can post in the relevant threads. — Martin Sleziak 1 min ago