"A" or "an" are troublesome in other ways. A recent battle arose in my bailiwick: an agreement was identified in a draft news release as being "AN historic document." When the draft was submitted to the public affairs professionals, it was purged of all "an" articles and substituted with "a."

The public affairs folks cited with great emphasis their source: the Associated Press Style Manual.

Grammarians around me are not happy with that; indeed, when the release was orally presented, and the speaker tried his best to evoke, "a historic," it cause disruption by the speaker who proceeded to edit on the fly with "an historic."