I trying some think like that /^[a-z]{6}|[a-z]{10}$/ but it work like /^[a-z]{6,}$/ ;] I need to match only 6 or 10..

Can anyone explain me why it work like that.. And make it works correctly ?

/^([a-z]{6}|[a-z]{10})$/ or /^[a-z]{6}$|^[a-z]{10}$/

Yap.. That was easy.. Now i understand the mistake Thank you.

And unless you're using $regml or $regsub to backreference, you should use:
/^([color:blue]?:[a-z]{6}|[a-z]{10})$/[/color]

Just a bit faster, telling the regex engine to group but not backref.