Spell-checking - MS Word/Internet

[Smokey Deza]

I'm confused.

MS Word 13 - The word 'spelt' is not flagged. Yet whilst typing it here - red wavy underscore.

The word 'costings'. Seems it's spelt correctly on here, but when I type in MS Word is it corrects with an apostrophe - 'costing's.'

Which is right?

 

[marc2003]

perhaps it's using american english?

 

[gillywibble]

Both are correct.