One L OR Two?

When I was in grade school, I learned the "Queen's English".

In other words, "proper" English.

What I have found in growing up and moving around the country is that Americans have not been taught proper English, and that popular media.  Simple things like the proper use of a comma, where to put punctuation when quotes are involved, when to use "which" vs. "that", when to use "whom" vs, "who" (though German helped reinforce that one)...

...but also when to double a letter when adding "ed".

This was always kind of hokey rule:  Add "ed" to a verb to make it past tense, EXCEPT if it already has an "e"...then you just add "d". Oh, and if you have a consonant before the "ed", you're supposed to double that consonant before adding "ed".

But the last one is only true some of the times.   And those times are different between American English and British English.

Examples are words like "cancelled" and "travelled" and "unravelled".

I learned these with two "l"s.

Americans spell these with one "l".

Both are considered correct spelling.

But it sure makes for interesting web development to have them spelled 1/2 one way and 1/2 the other.