I've spent some time thinking about this before, and it provides a clue about the writers accent. For example:
"An 'H'", and "a 'H'" are both equally valid following this rule (by my interpretation), depending on how you pronounce the letter 'H'.
Most English accents don't drop the "h" in herb, although American influence will change that.
But you can hear "an" used in phrases like "an hotel" or "an historic building", where the "h" is usually pronounced.
Most Americans don't pronounce the "h" in "herb" or "herbal" afaict. We do usually pronounce it in people's names though, like "Herb".
kichimi · · focus · HN ↗
"An 'H'", and "a 'H'" are both equally valid following this rule (by my interpretation), depending on how you pronounce the letter 'H'.
post-it · · focus · HN ↗
nephihaha · · focus · HN ↗
But you can hear "an" used in phrases like "an hotel" or "an historic building", where the "h" is usually pronounced.
isityettime · · focus · HN ↗