Unclear how to use Operators_fence special table #315

The Operators_fence special table has the entry {U+0331}, which taken at face value is the code point for a combining below macron. But that is clearly not a fence. It is, however, what you get for the content string "||" after applying Step 2.3 of the algorithm to determine the category of an operator.

Should this table then be utilized by first applying the above replacement to an input string before performing a lookup, or is this the only exception? Regardless of the answer, I think a comment explaining it should be added to the spec.