Not exactly what I had in mind, the antipattern is a simple test to distinguish between a phrase and a clause. In English, for the most part, introductory conjunctive adverbial, (or adjectival,) phrases are less than about 7 tokens long. After that, they tend to be clauses in their own right, (it makes a kind of logical sense if you think about it.)
If I just scan for a comma followed by an adverb then the number of false positives is quite high. On the other hand, if I eliminate any hits that are preceded by a phrase no longer than 7 tokens, I might miss a few genuine hits, but I cut the number of false positives drastically. In fact, any surviving false positives are frequently indicative of some other type of error. e.g. a misplaced comma; a missing article or pronoun; or simply poor phrasing and punctuation.
If the adverb forms a conjunction between two clauses, then the comma should normally be replaced by a semicolon.
A) the adverb forming a conjunction between two clauses
B) the comma being replaced
So, the corrected sentence reads:
If the adverb forms a conjunction between two clauses; then, the comma should normally be replaced by a semicolon.
Meanwhile, still beaming, Cindy dropped the plate.
Two introductory phrases with a single clause.
A) Meanwhile, an introductory adverbial phrase.
B) still beaming, an adjectival phrase that starts with the adverb 'still'
C) Cindy dropped the plate, the main clause.
As a result, in this 2nd example, (even though, the adverb 'still' follows a comma,) it is not a conjunction between two clauses and the comma is the correct punctuation. Actually, it would be completely wrong to use a semicolon in example 2.
In summary, what I am trying to do is find possible conjunctive adverbs, eliminate false positives by looking backwards upto 7 tokens for clausal punctuation; thus, verifying it is a conjunction of two clauses and not the conjunction of two phrases or a phrase and clause.
I hope that makes sense. It does to me, but at the moment I am so deeply involved in it that many of my friends politely reply: "Huh?"