How to tag someone who's username contains a space

Any ideas ?

I was trying to tag John M, but can't get it to work...

@john m

I wrote @ John M without the space between the @ and John.

Comes up on the page as [ MENTION=1307]john m after posting them going in to edit it. no space between the { and the M of mention

I wonder how it differentiates between a "john" and a "john m"

Just trying to write the name as it appears but putting an "AT" sign in front of it like ATbol takshin

@bol takshin

EDIT: that didn't work, now I'll try with correct capitalisation

@Bol Takshin

Didn't work, will try someone's username that's easier to spell, like ATMoa Hunter

@Moa Hunter

Heyy, that worked. Sorry Moa Hunter for waking you up.

Testing...
@Marty Henry

@john m