In response to Re the irrelevance of white man in Asia (Jerry L'épeire)

A comma, particularly when used to separate an interrupting dependent clause, is used in this
instance prior to an auxiliary form of the verb "to be" in conjunction with a
leading comma.

It is the opinion of most style manuals that a dependent clause situated prior to the subject is always preferable to separating the subject and verb-to-be with a comma-delimited phrase that ends immediately prior to the verb-to-be.

Grammatically permissible is not a prescription for good writing.

Compare:
When used to separate an interrupting dependent clause, a comma is used prior to an auxiliary form of the verb "to be" in conjunction with a leading comma.