This is a rant-
I mostly agree with McGrath. What dictionary, Kat?
It is a poor one if it doesn't classify its definitions.
The first category in Merriam Webster's covers two usages, a.An authoritative rule, esp: a rule for conduct of a liturgical service. b. second most common usage- a name, a title, specifically the title of a statute.
The second category 2. a. a heading or a part of a book or manuscript done differently from the rest (underlined, colored, etc.). This comes from the first usage, since headings and directions for divine service were usually printed in red. The third- 3. An established rule or custom (The order in the OED is different since it is based more on historical principles). A rubric to designate a man's name is another archaic usage.

"Ruberic," if in Google, is just an example of someone's ignorance or mis-spelling (Catspaw's usage excepted!).

Rubric for red ochre is archaic (still preserved as the first category in the OED because it is the root- red). There is a verb, rubricate, in print since the 16th century.

The example of a "rubric" linked above is part of what we used to call an outline guide, a reminder that helped us to keep thought ordered in an essay. Never heard one called a "rubric."

One form of rubricizing that should be punished by summary execution- highlighting of material in books.