I am reading "The Reader Over Your Shoulder" by Robert Graves (author of I, Claudius), which is a clarity\grace guide for written English. He has a section about punctuation, which gives examples of mistakes found in the wild. This is one of them:
"The fire of Prometheus is as a rush-light compared to the volcano of steam..."
The examination noting the punctuation error (one of many errors in this single sentence): "Without a comma at 'rush-light' it is the rush-light, not the fire of Prometheus, which is being compared to the volcano."
It's an interesting point, but I cannot find a further break down of this example (and how to use it) in my other grammar resources.
It is similar to how he pointed out the difference between these two sentences: "I did not go to the party, because I was not wanted" and "I did not go to the party because I was not wanted." The first one meaning what you think and the second meaning "I went to the party but the reason I went wasn't merely for the reason that I was not wanted (ie, I didn't go out of spite)." I had never heard of that usage either, though explanations of it were easier to find online than the rush-light example.