This is interesting - if I write "should've" (for "should have"), my spell checker underlines the word. Same happens if I do "could've" (for "could have"). I use these forms but I'm starting to question if there even is such form and if I'm using English correctly?
I also noticed that "I've" (for "I have") doesn't get underlines by the spell checker, but "things've" (for "things have") does.
Can anyone explain this?