You, sir, are a giant idiom!

[simple-smile]

Hej there,

I'm not a native speaker of English, but I enjoy the language a lot and always try to grasp as much as I can regarding expressions and idioms.

I've noticed on the forums that there's a lot of use of the phrase "they should of done that" or "I must of (checked the wrong box)", and I'd be curious if that is just shortwriting or internet slang, or if it's a common mistake. I believe it should be "they should've" or "I must have", right?

As a foreigner, I sure as hell won't raise a finger to correct native speakers, please understand this as a linguistic curiosity.